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Contribution of anti-ryanodine receptor antibody to impairment of excitation-contraction coupling in myasthenia gravis
Abstract
The aim of this study was to elucidate the relationship between the impairment of excitation-contraction (E-C) coupling and anti-ryanodine receptor (RyR) antibody in patients with myasthenia gravis (MG).
Masseteric compound muscle action potential (CMAP) and mandibular movement-related potentials (MRPs) were recorded simultaneously after stimulating the trigeminal motor nerve with a needle electrode. The E-C coupling time (ECCT) was calculated as the latency difference between CMAP and MRP. For each patient, we selected a representative data set when there was no abnormal decrement in response to repetitive nerve stimulation. The 26 data sets were divided into an anti-RyR-positive group (n=12) and an anti-RyR-negative group (n=14).
Masseteric ECCT was significantly longer (p=0.017) in anti-RyR-positive group (median, mean, range; 3.6, 3.8, 3.0-5.9 ms) than in anti-RyR-negative group (3.1, 3.1, 2.7-4.0) although there were no significant differences in masseteric CMAP amplitude and % decrement between the two groups. The bite force was significantly lower in anti-RyR-positive group than in normal controls.
Presence of anti-RyR antibodies is associated with significantly prolonged masseteric ECCT compared to absence of the antibodies in MG.
Anti-RyR antibody contributes to E-C coupling impairment in the masseter muscle in patients with MG.
... Studies suggest that having antibodies against ryanodine receptors is related to MGT and manifests mainly as delayed, severe MG. 21,22 MGT may render weakness due to damage to excitation-contraction coupling. 23 Having antibodies against LRP4 can cause muscular weakness: they can damage the structure of the neuromuscular junction and disturb the combination of agrin and LRP4 to influence accumulation of acetylcholine receptors. 24,25 Antibodies against Kvl4 mainly affect voltage-activated potassium channels on the surface of muscle fibers, thereby influencing membrane repolarization and maintenance of the resting potential. ...
... 24,25 Antibodies against Kvl4 mainly affect voltage-activated potassium channels on the surface of muscle fibers, thereby influencing membrane repolarization and maintenance of the resting potential. 23 Antibodies against acetylcholine are often present in MG patients who do not have antibodies against acetylcholine receptors and who have a poor reaction to the prostigmine test. A combination of antibody and synaptic acetylcholine inactivates acetylcholine and hinders its hydrolysis. ...
We report a case of ocular myasthenia gravis (MG) accompanied by anosmia. A 76-year-old man had idiopathic anosmia of 2-year duration. Four months before consultation, he began to have drooping in the right upper eyelid along with muscle soreness, distension, and pain in the nape. His tongue was dark-red with a thin and white coating; his pulse was wiry and slippery. According to Traditional Chinese Medicine, eyelid drooping and anosmia are the main signs of liver constraint and spleen deficiency. In Western Medicine, the diagnosis was ocular MG and idiopathic anosmia. Our patient, along with the literature, suggests that anosmia may be an early symptom before MG. MG accompanied by anosmia could be a special subtype of MG according to antibody production and symptoms.
... Finally, these filaments slide and muscle fiber length shortens [1][2][3] . In our previous studies [4][5][6][7] , we developed a novel method ( Imai's method) to estimate the time from muscle depolarization to initiation of muscle contraction. In Imai's method, masseteric compound muscle action potentials (CMAPs) and mandibular movement-related potentials (MRPs) are simultaneously recorded using an accelerometer, after trigeminal nerve stimulation with a needle electrode. ...
Objective:
The aim of this study was to apply a novel method to measure excitation-contraction coupling time (ECCT) in normal soleus muscles.
Methods:
We performed simultaneous recordings of soleus compound muscle action potential (CMAP) and foot movement-related potential (MRP), and measured ankle plantar flexion torque in 36 healthy subjects. We calculated ECCT and examined the relations between CMAP, MRP, ECCT and ankle plantar flexion torque.
Results:
Statistical analyses established reference ranges (mean ± SE) for CMAP (13.4 ± 0.9 mV), MRP (5.3 ± 0.4 m/s2), ECCT (5.2 ± 0.1 ms), torque (85.9 ± 6.4 Nm) and torque/body weight (1.4 ± 0.1 Nm/kg). The torque showed a positive linear correlation with CMAP (p = 0.041) and a negative linear correlation with ECCT (p = 0.045).
Conclusion:
Soleus ECCT can be recorded easily, and is useful to assess the impairment of E-C coupling in muscles of the lower extremities.
... Some MG patients have been shown to have impaired excitation-contraction coupling in addition to neuromuscular transmission failure. 22 The mechanisms of excitation-contraction coupling are closely related to RyR function, and anti-RyR antibodies might influence muscle contraction. ...
Anti‐striational antibodies (StrAbs) have been described as serum immunoglobulins that react with cross‐striations of skeletal muscle in patients with myasthenia gravis (MG). StrAbs were expected to be useful biomarkers of MG, however, because of their low specificity, the diagnostic utility of StrAbs has been limited. The main autoantigens of StrAbs included titin, ryanodine receptor, and Kv1.4. MG patients with StrAbs tend to suffer from bulbar symptoms and myasthenic crisis. The most remarkable finding of regarding the clinical significance of StrAbs is their association with myositis concomitant with MG. Myocarditis is the lethal complication in MG patients, but it is treatable by immunotherapy. Patients with myocarditis usually exhibit rapid deterioration with serious arrhythmias and severe heart failure. Since myocarditis often develops in patients with myositis accompanied by MG, MG with myositis and/or myocarditis is an important subset of patients. MG is one of the immune‐related adverse events (irAEs) associated with immune checkpoint inhibitors. MG with myositis and/or myocarditis is an infrequent subset of the patients in the usual clinical settings; however, it is more common in cases with irAEs. Anti‐titin and anti‐Kv1.4 antibodies were preferentially detected in patients with MG with myositis and/or myocarditis, and in patients with late‐onset and thymoma‐associated MG. The detection of StrAbs provides more specific and useful clinical information for the classification and management of MG patients and identifies diagnostic biomarkers of serious irAEs in cancer patients treated with immune checkpoint inhibitors.
... for anti-striational antibodies may be related to the false positive results of anti-ryanodine receptor antibodies. Anti-ryanodine receptor antibodies are involved in the disturbance of excitation-contraction coupling in skeletal muscle tissue 15 . On the other hand, our results suggest that the production of anti-ryanodine receptor antibodies may be a secondary phenomenon related to the muscle necrosis observed in immune-mediated necrotizing myopathy or muscular dystrophy. ...
The purposes of the present study were to identify anti-striational antibodies in myasthenia gravis (MG) patients with myositis and/or myocarditis using a combination of cell-based assays and flow cytometry (cytometric cell-based assays) and to describe the main clinical implications. Among 2,609 stored samples collected from all over Japan between 2003 and 2016, we had serum samples from 30 MG patients with myositis and/or myocarditis. Cytometric cell-based assays with titin, ryanodine receptor, and voltage-gated Kv1.4 were performed. Autoantibodies were determined by differences in phycoerythin fluorescence between the 293F cells and titin-transfected cells. MG patients with myositis and/or myocarditis as well as late-onset and thymoma-associated MG had anti-titin, anti-ryanodine receptor, and anti-Kv1.4 antibodies. In contrast, patients with early-onset MG, those with other myopathies and healthy controls did not have anti-titin or anti-Kv1.4 antibodies with some exceptions, but they possessed anti-ryanodine receptor antibodies. Thirty MG patients with myositis and/or myocarditis showed a severe generalized form, and 21 of them had thymoma. Anti-titin and anti-Kv1.4 antibodies were found in 28 (93%) and 15 (50%) patients, respectively, and all patients had at least one of these antibodies. Cytometric cell-based assays thus demonstrated that anti-striational antibodies are biomarkers of MG with myositis and/or myocarditis.
... In one study patients with RyR1 antibodies exhibit increased "excititation-contraction coupling latency" defined as the time between trigeminal nerve stimulation and masseteric compound muscle action potentials. However, the mechanism for this dyfunction is not well understood [139]. ...
Regulation of intracellular calcium (Ca2+) is critical in all cell types. The ryanodine receptor (RyR), an intracellular Ca2+ release channel located on the sarco/endoplasmic reticulum (SR/ER), releases Ca2+ from intracellular stores to activate critical functions including muscle contraction and neurotransmitter release. Dysfunctional RyR-mediated Ca2+ handling has been implicated in the pathogenesis of inherited and non-inherited conditions including heart failure, cardiac arrhythmias, skeletal myopathies, diabetes, and neurodegenerative diseases. Here we have reviewed the evidence linking human disorders to RyR dysfunction and describe novel approaches to RyR-targeted therapeutics.
... An increase in Fkbp5 would reduce influx of calcium and negatively impact muscle contractility. Muscle force generation is also reduced in isolated muscle preparations treated with sera from patients with MG (Imai et al., 2011(Imai et al., , 2012. In EDL, Zfn28 was found to be increased. ...
The differential susceptibility of skeletal muscle by myasthenia gravis (MG) is not well understood. We utilized RNA expression profiling of extraocular muscle (EOM), diaphragm (DIA), and extensor digitorum (EDL) of rats with experimental autoimmune MG (EAMG) to evaluate the hypothesis that muscles respond differentially to injury produced by EAMG. EAMG was induced in female Lewis rats by immunization with acetylcholine receptor purified from the electric organ of the Torpedo. Six weeks later after rats had developed weakness and serum antibodies directed against the AChR, animals underwent euthanasia and RNA profiling performed on DIA, EDL, and EOM. Profiling results were validated by qPCR. Across the three muscles between the experiment and control groups, 359 probes (1.16%) with greater than 2-fold changes in expression in 7 of 9 series pairwise comparisons from 31,090 probes were identified with approximately two-thirds being increased. The three muscles shared 16 genes with increased expression and 6 reduced expression. Functional annotation demonstrated that these common expression changes fell predominantly into categories of metabolism, stress response, and signaling. Evaluation of specific gene function indicated that EAMG led to a change to oxidative metabolism. Genes related to muscle regeneration and suppression of immune response were activated. Evidence of a differential immune response among muscles was not evident. Each muscle had a distinct RNA profile but with commonality in gene categories expressed that are focused on muscle repair, moderation of inflammation, and oxidative metabolism.
... Патогенетическая роль антител к RyR заключается в аллостерическом ингибировании рецепторов с последующим нарушением высвобождения ионов кальция из саркоплазматического ретикулума в ответ на возбуждение сарколеммы [54]. Недостаточный выброс кальция в цитоплазму приводит к нарушению функционирования актиномиозинового комплекса и, таким образом, к разобщению процессов возбуждения и сокращения мышечного волокна [56]. А. Mygland и соавт. ...
Myasthenia gravis is a classic autoimmune disease, which clinical manifestations in the form of weakness and abnormal muscle fatigue, due to the damaging effect of polyclonal antibodies to different structures of the neuromuscular synapse and muscles. The study of autoimmune substrate with myasthenia is routine in many clinics dealing with the problems of neuromuscular pathology, and the identification of high concentration of serum antibodies to a number of antigenic structures is the gold standard in diagnosis.Determination of serum antibodies to various autoimmune targets is an important tool in clinical practice. The majority of patients shows the high concentration of antibodies to AchR that gives the opportunity to use it as an important diagnostic criterion. The specificity of changes in the concentration of AchR-antibodies due to pathogenetic treatment allows to objectify the suppression of autoimmune aggression and evaluate the reliability of remission. However, the absence of AchR-antibodies when there are clear clinical and electromyography signs of myasthenia gravis suggests an autoimmune attack against a number of other targets, the most studied of which is the MuSK. On the contrary, patients with myasthenia gravis associated with thymoma, almost always have a higher level of AchR-antibodies. The presence of thymoma is accompanied by the generation of antibodies to titin and RyR, which is also observed in persons with late-onset myasthenia without thymoma. High concentration of antibodies to these structures can be interpreted as a reliable sign of thymoma in patients younger than 60 years.
... Antibodies against K V 1.4 are also responsible for cardiac dysfunction like lethal arrhythmia, tachycardia, sick sinus syndrome, atrial ventricular block, prolonged QT time and myocarditis along with neurological complication in MG [207,208]. Circulating anti-RyR (Ryanodine receptor) antibodies are responsible for impaired (prolonged) excitationcontraction coupling in cardiac muscles and the severe form of thymoma in MG [209] because RyR activates VGCC (dihydropyridine receptor), mediates calcium release from sarcoplasmic reticulum and regulates Excitation-Contraction Coupling Time (EC-CT) [210]. In severe cases autoantibodies against TRPC3 are also present which is believed to be associated with RyR antibodies and regulates EC-CT coupling [211]. ...
Ion channels are integral membrane proteins that orchestrate the passage of ions across the cell membrane and thus regulate the various key physiological processes of the living system. The stringently regulated expression and function of these channels hold a pivotal role in the development and execution of various cellular functions.Malfunction of these channels result in debilitating diseases collectively termed channelopathies. In this review we highlight the role of these proteins in the immune system with special emphasis on the development of autoimmunity. The role of ion channels in various autoimmune diseases is also listed out. This comprehensive review summarises the ion channels that could be used as molecular targets in the development of new therapeutics against auto immune disorders.
... Myasthenia gravis is an autoimmune disease characterized by muscle weakness secondary to destruction of nicotinic acetylcholine receptors. In a recent study patients with autoantibodies targeting RyR1 had significantly worse EC-coupling impairment than those without these antibodies [59]. Methods for detecting RyR1 antibodies may serve as a prognostic indicator for patients with myasthenia gravis [60]. ...
Research over the past two decades has implicated dysfunction of the ryanodine receptor (RyR), a Ca2+ release channel on the sarcoplasmic reticulum (SR) required for excitation-contraction (EC) coupling, in the pathogenesis of cardiac and skeletal myopathies. These discoveries have led to the development of novel drugs, screening tools, and research methods. The patents associated with these advances tell the story of the initial discovery of RyRs as a target for plant alkaloids, to their central role in cardiac and skeletal muscle excitation-contraction coupling, and ongoing clinical trials with a novel class of drugs called RycalsTM that inhibit pathological intracellular Ca2+ leak. Additionally, these patents highlight questions, controversies, and future directions of the RyR field.
Background:
The clinical manifestations and prognosis of myasthenia gravis are related to antibodies, and children are affected differently than adults. The presence of ryanodine receptor and titin antibodies in adults indicates late onset and severe disease related to thymoma, but their role in children is rarely reported.
Methods:
This study collected a cohort of children according to inclusion and exclusion criteria, consisting of antibody-negative, AChR-positive, and AChR with or without titin and RyR antibodies. The differences among groups in general conditions, clinical manifestation, treatment and prognosis were compared.
Results:
In total, 171 patients were included: 33 patients (19.30%) were antibody-negative, 84 patients (49.12%) were positve for AChR antibody, 22 patients (12.87%) were positve for AChR and RyR antibodies, 5 patients (2.92%) were positve for AChR and Titin antibodies, and 27 patients (15.79%) were positve for AChR, RyR and Titin antibodies. The median onset age of all the patients was 57.8 (9-177) months, and patients with AChR and RyR antibodies (p = 0.02) and AChR, RyR and Titin antibodies (p = 0.0006) had a younger onset age than patients with AChR antibodies. The rate of generalized MG and MG-ADL before treatment in the AChR-, RyR- and Titin antibody-positive groups was distinctly higher than that in the AChR antibody-positive group (p = 0.038, p = 0.0325). The rate of IVIG use in the AChR-, RyR- and Titin antibody-positive groups (p = 0.0388) was higher than that in the AChR antibody-positive group. The rate of immunosuppressant use in the AChR and RyR antibody-positive group (p = 0.0415) and in the AChR, RyR and Titin antibody-positive group (p = 0.0006) was higher than that in the AChR antibody-positive group. Plasmapheresis was performed in 1 case in the AChR-, RyR- and Titin antibody-positive groups. The CSR rate in the AChR and RyR antibody-positive group (p = 0.0423) and in the AChR, RyR and Titin antibody-positive group (p = 0.0152) was significantly lower than that in the AChR antibody-positive group. Gender, ptosis severity, and CSR time were not significantly different between groups.
Conclusions:
We summarized one of the largest cohorts of pediatric MG patients and compared the clinical phenotype of patients with antibody-negative, AChR-positive, and AChR with or without titin and RyR antibodies. The results showed that patients with AChR and RyR antibodies had a younger onset age, a higher immunosuppressant use rate and a lower CSR rate.
Objective
This study aimed to develop a simple and reliable technique to assess excitation-contraction (E-C) coupling for early diagnosis of critical illness myopathy (CIM).
Methods
We prospectively performed clinical and electrophysiological examinations on patients admitted to intensive care unit (ICU). In addition to full neurological examinations and routine nerve conduction study, motor related potential (MRP) was recorded using an accelerometer attached to the base of hallux after tibial nerve stimulation, and E-C coupling time (ECCT) was measured from the latency difference between soleus compound muscle action potential (CMAP) and MRP.
Results
Of 41 patients evaluated, 25 met the criteria for ICU-acquired weakness, 23 of whom had CIM. The time to the first electrophysiological examination (time to first test) correlated negatively with CMAP and with MRP. Conversely, a positive correlation was observed between the time to first test and ECCT. E-C coupling impairment occurred in most of our patients with CIM by the third day of ICU admission, and prolonged ECCT could be the earliest detectable abnormality.
Conclusions
The ECCT measurement is an easy and reliable technique to detect reduced muscle membrane excitability in the early stage of CIM.
Significance
The ECCT measured by our method using an accelerometer may be a parameter that predicts the development of CIM.
Background
Data on antibody profile in myasthenia gravis (MG) from India are limited.
Objectives
To investigate antibody profile in patients with MG and their clinical correlates.
Patients and Methods
Patients of MG (n=85, M:F::1.1:1, mean age: 39.29±17.3 years, mean symptom‐duration: 72.94±91.8 months) were evaluated for clinical features, MG foundation of America (MGFA) score, response to treatment and outcome at last follow‐up. Antibodies to acetylcholine receptor (AChR), muscle‐specific kinase (MUSK), titin and ryanodine‐receptor (RYR) were analysed using ELISA.
Results
Based on the regional distribution of weakness, the cohort could be categorized as: generalized: 60, ocular: 16 and oculo‐bulbar: 9. Sixty patients were followed up for a mean duration of 26.74±13.8 months. Outcome at last follow‐up was: remission‐ 22, no remission‐ 33, dead‐ 5. AChR‐ and MUSK‐antibodies were detected in 58 and 8 patients respectively. Frequency of generalized MG, worse MGFA during the antibodies, though outcome at last follow‐up was comparable between AChR‐antibody positive and negative disease course and thymomatous histology significantly correlated with presence of AChR‐ groups. Patients with MUSK‐antibodies had oculo‐bulbar or generalized MG and frequent respiratory crisis, but majority improved or remitted with treatment. Titin‐antibodies were detected in 31.8% and RYR‐antibodies in 32.9%. Their presence did not correlate with age at onset of MG, severity or presence of thymoma.
Conclusion
This report highlights the spectrum of antibodies in MG in an Indian cohort. AChR‐antibody positivity correlated with clinical severity. Outcome was good in majority of MUSK‐antibody positive MG. The role of other antibodies, complementary vs epiphenomenon, remains open.
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Objective:
The aim of this study was to evaluate post-tetanic potentiation of muscle twitch in myasthenia gravis (MG).
Methods:
Post-tetanic potentiation was evaluated by recording the compound muscle action potential (CMAP) of abductor pollicis brevis and movement-related potential (MRP) of the thumb using an accelerometer after tetanic stimulation of the median nerve at the wrist. After baseline recording, tetanic stimulation was delivered to the median nerve at a frequency of 10Hz for 10s. The CMAP and MRP were successively recorded at baseline and at 5, 10, 30, 60, 90 and 120s after tetanic stimulation. The chronological changes of CMAPs and MRPs were recorded bilaterally in 11 patients with MG, 9 patients with myopathies (disease controls), and 25 healthy control subjects.
Results:
Maximal acceleration of MRP was significantly elevated during 10s after tetanic stimulation without any CMAP changes in all groups. However, statistical analysis detected a significant decrease in post-tetanic potentiation of maximal acceleration of MRP in MG patients only compared to healthy controls, but not in myopathy patients, which may imply impairment of excitation-contraction coupling in MG.
Conclusions:
Post-tetanic potentiation of muscle twitch is significantly diminished in MG, suggesting impaired excitation-contraction coupling.
Significance:
Measurement of post-tetanic potentiation using an accelerometer is a simple and sensitive method to detect impairment of excitation-contraction coupling in MG.
Objective
The aim of this study was to compare the characteristics of myasthenic patients with and without thymoma, and the results of thymectomy in both types of patients.
Material and methods
A retrospective study was conducted among 66 patients who underwent thymectomy for myasthenia gravis in our department over a 10-year period (2000–2010). The surgical approach was sternotomy or anterolateral thoracotomy. Patients were divided into two groups according to the presence of thymoma: with (T-MG) and without (NT-MG) thymoma. Complete stable remission (CSR) was the primary endpoint.
Results
Median age was 35.09 ± 9.89 years. The NT-MG group had 38 patients (57.57%) and the T-MG group 28 patients (42.43%). There was no difference between the two groups regarding the surgical approach (P = 0.52). T-MG patients were older (40.54 ± 15.16 vs. 31.37 ± 9.46) (P = 0.008) and predominantly male. There were more generalized forms (P = 0.01) and more bulbar involvement (P = 0.02) in the T-MG group. The rate of CSR at 5 years was 7% and 17% in the T-MG and NT-MG patients respectively (P = 0.70). At 10 years, it was 36% and 94.73% respectively (P = 0.03).
Conclusion
Thymomatous myasthenia gravis is characterized by the severity of its clinical features. Remission rate at 10 years was significantly lower in the myasthenia with thymoma group.
OBJECTIVE: The aim of this study was to compare the characteristics of myasthenic patients with and without thymoma, and the results of thymectomy in both types of patients. MATERIAL AND METHODS: A retrospective study was conducted among 66 patients who underwent thymectomy for myasthenia gravis in our department over a 10-year period (2000-2010). The surgical approach was sternotomy or anterolateral thoracotomy. Patients were divided into two groups according to the presence of thymoma: with (T-MG) and without (NT-MG) thymoma. Complete stable remission (CSR) was the primary endpoint. RESULTS: Median age was 35.09±9.89years. The NT-MG group had 38 patients (57.57%) and the T-MG group 28 patients (42.43%). There was no difference between the two groups regarding the surgical approach (P=0.52). T-MG patients were older (40.54±15.16 vs. 31.37±9.46) (P=0.008) and predominantly male. There were more generalized forms (P=0.01) and more bulbar involvement (P=0.02) in the T-MG group. The rate of CSR at 5years was 7% and 17% in the T-MG and NT-MG patients respectively (P=0.70). At 10years, it was 36% and 94.73% respectively (P=0.03). CONCLUSION: Thymomatous myasthenia gravis is characterized by the severity of its clinical features. Remission rate at 10years was significantly lower in the myasthenia with thymoma group.
抄録
We have developed a new novel method to assess the function of excitation-contraction (E-C) coupling in patients with myasthenia gravis (MG). In our procedure, masseteric compound muscle action potential (CMAP) and mandibular movement-related potentials (MRP) were recorded simultaneously after stimulating the trigeminal motor nerve with a needle electrode. The E-C coupling time (ECCT) was calculated by the latency difference between CMAP and MRP. Bite force was measured using a pressure-sensitive sheet. Our serial studies demonstrate that masseteric E-C coupling is impaired in some MG patients, and functional recovery of E-C coupling contributes at least in part to the increase in bite force after treatment. We also reveal that presence of anti-RyR antibodies is associated with significantly prolonged masseteric ECCT compared to absence of the antibodies in MG, and tacrolimus (FK506) induces ECCT shortening accompanying clinical improvement within 2 weeks. These results indicate the contribution of anti-ryanodine receptor (RyR) antibody to E-C coupling impairment, and the early effect of tacrolimus as a pharmacological enhancement of RyR function to improve E-C coupling in MG. In further studies, the present method may be applied to assess the post-tetanic potentiation of E-C coupling in human skeletal muscles.
Tacrolimus (FK506) is a macrolide T-cell immunomodulator used to treat myasthenia gravis (MG). Besides immunosuppression, tacrolimus has been reported to have the potential to increase muscle strength by enhancing ryanodine receptor (RyR) function. However, few attempts have been made to demonstrate the early effect of tacrolimus as an RyR enhancer in clinical investigation.
In 20 MG patients, masseteric compound muscle action potential (CMAP) and mandibular movement-related potentials (MRPs) were recorded simultaneously after stimulating the trigeminal motor nerve with a needle electrode. The excitation-contraction (E-C) coupling time (ECCT) was calculated by the latency difference between CMAP and MRP. Bite force was measured using a pressure-sensitive sheet. Serial assessments of % decrement in masseteric repetitive nerve stimulation (RNS), ECCT and bite force were performed before and within 4 weeks of tacrolimus (3 mg day(-1)) treatment. The median (mean, range) interval of assessment was 2 (2.4, 1-4) weeks. We also measured serum antibodies against RyR, acetylcholine receptor and muscle-specific receptor tyrosine kinase.
Bite force increased after tacrolimus treatment accompanying clinical improvement assessed by Myasthenia Gravis Foundation of America classification, but the bite force difference did not reach statistical significance. Wilcoxon matched-pairs signed-ranks test detected a significant ECCT shortening in 12 patients assessed after 1-2 weeks of tacrolimus treatment as well as in eight patients assessed after 3-4 weeks. In contrast, masseteric CMAP and % decrement showed no significant changes after short-term tacrolimus treatment.
Tacrolimus induces ECCT shortening accompanying clinical improvement despite no improvement in % decrement within 2 weeks.
This early effect of tacrolimus may imply a pharmacological enhancement of RyR function to improve E-C coupling in MG.
We have cloned cDNAs encoding the rabbit and human forms of the Ca2+ release channel of sarcoplasmic reticulum. The human cDNA encodes a protein of 5032 amino acids, with a molecular weight of 563,584, which is made without an NH2-terminal signal sequence. Amino acid substitutions between rabbit and human sequences were noted in 163 positions and deletions or insertions in eight regions accounted for additional sequence differences between the two proteins. Analysis of the sequence indicates that 10 potential transmembrane sequences in the COOH-terminal fifth of the molecule and two additional, potential transmembrane sequences nearer to the center of the molecule could contribute to the formation of the Ca2+ conducting pore. The remainder of the molecule is hydrophilic and presumably constitutes the cytoplasmic domain of the protein. A 114-120 amino acid motif is repeated four times in the protein, in residues 841-954, 955-1068, 2725-2844, and 2845-2958 and a 16 amino acid part of the motif is repeated twice more in residues 1344-1359 and 1371-1386. Although the channel is modulated by Ca2+, ATP, and calmodulin, no clear high affinity Ca2(+)-binding domain of the EF hand type and no clear high affinity ATP-binding domain were detected in the primary sequence. An acidic sequence in residues 1872-1923 contains 79% glutamate or aspartate residues and this sequence is a potential low affinity Ca2(+)-binding site. Several potential calmodulin-binding sites were observed in the sequence, in the region 2800 to 3050.
Interactions between the Ca2+release channel of skeletal muscle sarcoplasmic reticulum (ryanodine receptor or RyR1) and the loop linking domains II and
III (II-III loop) of the skeletal muscle l-type Ca2+ channel (dihydropyridine receptor or DHPR) are critical for excitation-contraction coupling in skeletal muscle. The DHPR
II-III loop was fused to glutathione S-transferase- or His-peptide and used as a protein affinity column for 35S-labeledin vitro translated fragments from the N-terminal three-fourths of RyR1. RyR1 residues Leu922–Asp1112 bound specifically to the DHPR II-III loop column, but the corresponding fragment from the cardiac ryanodine receptor (RyR2)
did not. The use of chimeras between RyR1 and RyR2 localized the interaction to 37 amino acids, Arg1076–Asp1112, in RyR1. The RyR1 922–1112 fragment did not bind to the cardiac DHPR II-III loop but did bind to the skeletal muscle Na+ channel II-III loop. The skeletal DHPR II-III loop double mutant K677E/K682E lost most of its capacity to interact with RyR1,
suggesting that two positively charged residues are important in the interaction between RyR and DHPR.
Electrical and mechanical muscular responses to single and repetitive stimuli were recorded in 24 patients with myasthenia gravis. Findings in the platysma were compared with those in m. adductor pollicis (ADP). In the platysma, but not in the ADP, electrical and mechanical responses to single stimuli were often lower than normal, and could be normalised after tetanus and by endrophonium. The decrement of electrical and mechanical responses to repetitive stimuli was two to three times greater in the platysma than in the ADP; post-tetanic facilitation of the action potential was four times greater. The staircase phenomenon was abnormal in the platysma in patients with moderate and severe myasthenia, and also in the ADP in some patients without decrement in the action potential. Edrophonium was more effective in alleviating decrement in the platysma than in the ADP. In the platysma, block of neuromuscular transmission could account for most abnormalities. The finding in some patients of an abnormal staircase after correction for block of fibres indicates a lesion in excitation-contraction coupling. In six patients only the platysma showed abnormalities, in 10 patients abnormalities were more pronounced in the platysma than in the ADP, and in three patients more pronounced in the ADP than in the platysma; in five patients the platysma and the ADP were equally affected.
In the platysma of 34 normal subjects the amplitude of the action potential and twitch tension and tetanic tension were lower, the contraction time of the isometric twitch was 1.4 times shorter, and the potentiation of twitch tension in a staircase and after tetanus was two to four times greater than in m. adductor pollicis. Differences in twitch kinetics and potentiation were related to the four times higher incidence of fast fibres in the platysma than in the adductor pollicis muscle, as determined by histochemistry. Ninety-five per cent confidence limits were established for comparison with patients with myasthenia gravis.
The ryanodine receptor has been purified from junctional terminal cisternae of fast skeletal muscle sarcoplasmic reticulum (SR). The ryanodine receptor was solubilized with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) and stabilized by addition of phospholipids. The solubilized receptor showed the same [3H]ryanodine binding properties as the original SR vesicles in terms of affinity, Ca2+ dependence, and salt dependence. Purification of the ryanodine receptor was performed by sequential column chromatography on heparin-agarose and hydroxylapatite in the presence of CHAPS. The purified receptor bound 393 +/- 65 pmol of ryanodine/mg of protein (mean +/- S.E., n = 5). The purified receptor showed three bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Mr of 360,000, 330,000, and 175,000. Densitometry indicates that these are present in the ratio of 2/1/1, suggesting a monomer Mr of 1.225 X 10(6) and supported by gel exclusion chromatography in CHAPS. Electron microscopy of the purified preparation showed the square shape of 210 A characteristic of and comparable in size and shape to the feet structures of junctional terminal cisternae of SR, indicating that ryanodine binds directly to the feet structures. From the ryanodine binding data, the stoichiometry between ryanodine binding sites to the number of feet structures is estimated to be about 2. Since the ryanodine receptor is coupled to Ca2+ gating, the present finding suggests that the ryanodine receptor and Ca2+ release channel represent a functional unit, the structural unit being the foot structure which, in situ, is junctionally associated with the transverse tubules. It is across this triad junction that the signal for Ca2+ release is expressed. Thus, the foot structure appears to directly respond to the signal from transverse tubules, causing the release of Ca2+ from the junctional face membrane of the terminal cisternae of SR.
We have developed a procedure to isolate, from skeletal muscle, enriched terminal cisternae of sarcoplasmic reticulum (SR), which retain morphologically intact junctional "feet" structures similar to those observed in situ. The fraction is largely devoid of transverse tubule, plasma membrane, mitochondria, triads (transverse tubules junctionally associated with terminal cisternae), and longitudinal cisternae, as shown by thin-section electron microscopy of representative samples. The terminal cisternae vesicles have distinctive morphological characteristics that differ from the isolated longitudinal cisternae (light SR) obtained from the same gradient. The terminal cisternae consist of two distinct types of membranes, i.e., the junctional face membrane and the Ca2+ pump protein-containing membrane, whereas the longitudinal cisternae contain only the Ca2+ pump protein-containing membrane. The junctional face membrane of the terminal cisternae contains feet structures that extend approximately 12 nm from the membrane surface and can be clearly visualized in thin section through using tannic acid enhancement, by negative staining and by freeze-fracture electron microscopy. Sections of the terminal cisternae, cut tangential to and intersecting the plane of the junctional face, reveal a checkerboardlike lattice of alternating, square-shaped feet structures and spaces each 20 nm square. Structures characteristic of the Ca2+ pump protein are not observed between the feet at the junctional face membrane, either in thin section or by negative staining, even though the Ca2+ pump protein is observed in the nonjunctional membrane on the remainder of the same vesicle. Likewise, freeze-fracture replicas reveal regions of the P face containing ropelike strands instead of the high density of the 7-8-nm particles referable to the Ca2+ pump protein. The intravesicular content of the terminal cisternae, mostly Ca2+-binding protein (calsequestrin), is organized in the form of strands, sometimes appearing paracrystalline, and attached to the inner face of the membrane in the vicinity of the junctional feet. The terminal cisternae preparation is distinct from previously described heavy SR fractions in that it contains the highest percentage of junctional face membrane with morphologically well-preserved junctional feet structures.
The ryanodine receptor/calcium release channel (CRC) of rabbit skeletal muscle terminal cisternae (TC) of sarcoplasmic reticulum (SR) has been found to be tightly associated with FK-506 binding protein (FKBP-12), the cytosolic receptor (immunophilin) for the immunosuppressant drug FK-506 (Jayaraman, T., Brillantes, A. M., Timerman, A. P., Fleischer, S., Erdjument-Bromage, H., Tempst, P., and Marks, A. (1992) J. Biol. Chem. 267, 9474-9477). In this study, a procedure is described to dissociate FKBP from TC and reconstitute human recombinant FKBP-12 back to the ryanodine receptor so that the role of the immunophilin on CRC activity can be assessed. Titration of TC vesicles with FK-506 dissociates FKBP from the ryanodine receptor. Sedimentation of FK-506-treated vesicles effectively separates the TC from the soluble FKBP-FK506 complex which remains in the supernatant. The FKBP-deficient TC vesicles have altered functional characteristics: 1) the ATP-stimulated calcium uptake rate of TC vesicles is reduced 2-fold; and 2) the threshold concentration of caffeine required to induce calcium release from TC vesicles is decreased. These changes appear to reflect modification of the calcium release channel since: 1) severalfold higher concentrations of FK-506 do not alter the calcium uptake rate of either longitudinal tubules of SR, or TC vesicles in the presence of ruthenium red; 2) human recombinant FKBP reassociates with FKBP-deficient TC but not with control TC or longitudinal tubules of SR; and 3) the reduced Ca2+ uptake rate in FKBP-deficient TC is restored to control values in the FKBP-reconstituted TC. These studies demonstrate that FKBP-12 modulates the CRC of rabbit skeletal muscle sarcoplasmic reticulum.
Excitation-contraction coupling in skeletal muscle is a result of the interaction between the Ca²⁺ release channel of skeletal muscle sarcoplasmic reticulum (ryanodine receptor or RyR1) and the skeletal muscle L-type Ca²⁺ channel (dihydropyridine receptor or DHPR). Interactions between RyR1 and DHPR are critical for the depolarization-induced activation of Ca²⁺ release from the sarcoplasmic reticulum, enhancement of DHPR Ca²⁺ channel activity, and repolarization-induced inactivation of RyR1. The DHPR III–IV loop was fused to glutathione S-transferase (GST) or His-peptide and used as a protein affinity column for³⁵S-labeled, in vitro translated fragments from the N-terminal three-fourths of RyR1. RyR1 residues Leu⁹²²–Asp¹¹¹² bound specifically to the DHPR III–IV loop column, but the corresponding fragment from the cardiac ryanodine receptor (RyR2) did not. Construction of chimeras between RyR1 and RyR2 showed that amino acids Lys⁹⁵⁴–Asp¹¹¹² retained full binding activity, whereas Leu⁹²²–Phe¹⁰⁷⁵ had no binding activity. The RyR1 sequence Arg¹⁰⁷⁶–Asp¹¹¹², previously shown to interact with the DHPR II–III loop (Leong, P., and MacLennan, D., H. (1998) J. Biol. Chem. 273, 7791–7794), bound to DHPR III–IV loop columns, but with only half the efficiency of binding of the longer RyR1 sequence, Lys⁹⁵⁴–Asp¹¹¹². These data suggest that the site of DHPR III–IV loop interaction contains elements from both the Lys⁹⁵⁴–Phe¹⁰⁷⁵ and Arg¹⁰⁷⁶–Asp¹¹¹² fragments. The presence of 4 ± 0.4 μm GST-DHPR II–III or 5 ± 0.1 μm His-peptide-DHPR III–IV was required for half-maximal co-purification of ³⁵S-labeled RyR1 Leu⁹²²–Asp¹¹¹² on glutathione-Sepharose or Ni²⁺-nitrilotriacetic acid. Dose-dependent inhibition of ³⁵S-labeled RyR1 Leu⁹²²–Asp¹¹¹² binding to GST-DHPR II–III and GST-DHPR III–IV by His10-DHPR II–III and His-peptide-DHPR III–IV was observed. These studies indicate that the DHPR II–III and III–IV loops bind to contiguous and possibly overlapping sites on RyR1 between Lys⁹⁵⁴ and Asp¹¹¹².
The authors have developed an MG activities of daily living (ADL) profile (MG-ADL)-a simple eight-question survey of MG symptoms. In 254 consecutive encounters with established MG patients, the authors compared scores from the MG-ADL to the quantitative MG score (QMG)-a standardized, reliable scale used in clinical trials. The mean MG-ADL score was 4.89+/-3.63. The mean QMG score was 10.80+/-5.70. Pearson's correlation coefficient was 0.583 (p < 0.001). The MG-ADL is an easy-to-administer survey of MG that correlates well with the QMG and can serve as a secondary efficacy measurement in clinical trials.
The aim of this study was to estimate normal jitter in voluntarily activated extensor digitorum communis (EDC) and orbicularis oculi (OOc) muscles using a disposable concentric needle electrode (CNE). The EDC of 67 normal subjects (22 males and 45 females, mean age 35.5 +/- 10.2 years) and the OOc of 50 normal subjects (13 males and 37 females, mean age 37.9 +/- 9.6 years) were studied. Jitter values were expressed as the mean consecutive difference (MCD) of 20 potential pairs. The mean MCD for EDC was 23.6 +/- 3.1 micros (upper 95% confidence limit [CL]: 29.7 micros). The mean MCD of all potential pairs (n = 1340) was 23.5 +/- 7.3 micros (95% CL: 38.2 micros). The mean MCD for the 18th highest value was 31.4 +/- 4.9 micros (95% CL: 41.2 micros). The mean MCD for OOc was 24.7 +/- 3.1 micros (95% CL: 31.0 micros). The mean MCD of all potential pairs (n = 1000) was 24.7 +/- 7.1 micros (95% CL: 39.0 micros). The mean MCD for the 18th highest value was 32.7 +/- 4.1 micros (95% CL: 40.9 micros). Our reported CNE jitter values obtained during voluntary activation represent the largest series currently available. The suggested practical limit in the EDC for mean MCD was 30 mus and for outliers was 42 micros, and in the OOc for mean MCD was 31 micros and 41 micros for outliers. The present study confirms that CNE can be used to assess jitter values, although certain precautions must be taken.
We have developed a procedure to isolate, from skeletal muscle, enriched terminal cisternae of sarcoplasmic reticulum (SR), which retain morphologically intact junctional "feet" structures similar to those observed in situ. The fraction is largely devoid of transverse tubule, plasma membrane, mitochondria, triads (transverse tubules junctionally associated with terminal cisternae), and longitudinal cisternae, as shown by thin-section electron microscopy of representative samples. The terminal cisternae vesicles have distinctive morphological characteristics that differ from the isolated longitudinal cisternae (light SR) obtained from the same gradient. The terminal cisternae consist of two distinct types of membranes, i.e., the junctional face membrane and the Ca2+ pump protein-containing membrane, whereas the longitudinal cisternae contain only the Ca2+ pump protein-containing membrane. The junctional face membrane of the terminal cisternae contains feet structures that extend approximately 12 nm from the membrane surface and can be clearly visualized in thin section through using tannic acid enhancement, by negative staining and by freeze-fracture electron microscopy. Sections of the terminal cisternae, cut tangential to and intersecting the plane of the junctional face, reveal a checkerboardlike lattice of alternating, square-shaped feet structures and spaces each 20 nm square. Structures characteristic of the Ca2+ pump protein are not observed between the feet at the junctional face membrane, either in thin section or by negative staining, even though the Ca2+ pump protein is observed in the nonjunctional membrane on the remainder of the same vesicle. Likewise, freeze-fracture replicas reveal regions of the P face containing ropelike strands instead of the high density of the 7-8-nm particles referable to the Ca2+ pump protein. The intravesicular content of the terminal cisternae, mostly Ca2+-binding protein (calsequestrin), is organized in the form of strands, sometimes appearing paracrystalline, and attached to the inner face of the membrane in the vicinity of the junctional feet. The terminal cisternae preparation is distinct from previously described heavy SR fractions in that it contains the highest percentage of junctional face membrane with morphologically well-preserved junctional feet structures.
Mastication was evaluated in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in remission who previously suffered from bulbar symptoms, and healthy controls. Bulbar myasthenia gravis may impair mastication due to weakness of the masticatory muscles. The aim of the study was to objectively evaluate the influence of myasthenia gravis on mastication. The subjects chewed a piece of breakfast cake and chewed 1 min on a piece of chewing gum. Surface EMG of the masseter muscle, temporalis muscle and jaw opener muscles was recorded. Statistical analysis revealed that bulbar patients produced significantly less EMG activity in the closing phase of a chewing cycle in both experiments. The EMG of the masseter muscle expressed as percentage of the maximum EMG during maximal clenching showed significantly higher values in the bulbar group than in the other groups. This was not found for the temporalis muscle. It was suggested that bulbar patients use a strategy of limited effort to produce a bolus that can be swallowed. The ocular patients and the patients in remission showed no subclinical impairments in muscle function during chewing.
Masticatory muscle strength was quantified in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in clinical remission (whether or not pharmacological) who previously suffered from bulbar myasthenia gravis, and healthy subjects. Maximal bite force and maximal activity of the masseter and temporalis muscles and of the submental muscle complex were measured. Bite force was decreased in the patients with bulbar myasthenia gravis, but was normal in the patients in the clinical remission group and in the ocular group. These findings were consistent with the results of electromyographic data. Although subjective reports of masticatory muscle weakness provide valuable information, quantitative measurements provide more information about the degree of muscle weakness of individual muscles. This is especially important for longitudinal evaluation of therapy in individual patients and for pharmacotherapeutic research. © 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 1694–1699, 2000.
Patients with myasthenia gravis can have antibodies against skeletal muscle ryanodine receptor (Ry1), the sarcoplasmic reticulum calcium-release channel, which plays a crucial role in excitation–contraction coupling. We have screened a panel of overlapping Ry1 fusion proteins with Ry1 antibody–containing myasthenia gravis sera to identify the main immunogenic region. The pc2 Ry1 fusion protein representing a Ry1 region close to the N-terminus (residues 799–1172) was identified as the main immunogenic region for the antibodies. The binding kinetics of the Ry1 antibodies to the pc2 Ry1 fusion protein were tested using an optical biosensor. Ry1 antibodies in the IgG fraction from sera of patients with myasthenia gravis bound with high affinity and with a stoichiometry of 1:1. The functional effect of these Ry1 antibodies was tested in an in vitro Ca2+-release assay. The Ry1 antibodies induced a twofold increase of the half-maximal concentration for 4-Cl-m-cresol–induced Ca2+ release from terminal cisternae vesicles but had no effect on Vmax. The effect on 4-Cl-m-cresol–induced Ca2+ release was specific, as preincubation of the active IgG fraction with the pc2 Ry1 fusion protein abolished the inhibition. These data suggest that the Ry1 sequence defined by residues 799–1172 is involved in the regulation of Ry1 function, and that this regulation could be functionally affected in vivo in patients with myasthenia gravis. Muscle Nerve 27: 81–89, 2003
The aim of this study was to elucidate the relationship between the impairment of excitation-contraction (E-C) coupling of masseter and the bite force in patients with myasthenia gravis (MG).
In 20 patients with MG, masseteric compound muscle action potential (CMAP) and mandibular movement-related potentials (MRP) were recorded simultaneously after stimulating the trigeminal motor nerve with a needle electrode. The E-C coupling time (ECCT) was calculated by the latency difference between CMAP and MRP. Bite force was measured using a pressure-sensitive sheet. Serial assessments of % decrement in masseteric repetitive nerve stimulation (RNS), ECCT, and bite force were performed before and after corticosteroid therapy alone or in various combinations with FK506, cyclosporin A, intravenous immunoglobulin and immunoabsorption.
Percent amplitude decrement in RNS and ECCT decreased significantly accompanying an increase in bite force after treatment. Simple regression analysis demonstrated a linear correlation among % decrement, ECCT and bite force. However, ECCT shortening accompanying bite force recovery without reduction in % decrement was observed in 4 patients.
Masseteric E-C coupling is impaired in some MG patients, and functional recovery of E-C coupling contributes at least in part to the increase in bite force after treatment.
Impaired E-C coupling contributes to muscle weakness in patients with MG.
To investigate autoantibodies related to excitation-contraction (E-C) coupling in patients with myasthenia gravis (MG), we developed a novel method to detect autoantibodies against dihydropyridine receptor (DHPR). Using this method, we detected DHPR antibody in 37% (11 out of 30) of MG patients with thymoma. Antibodies were not detected in normal nor disease controls. The titer of DHPR antibodies showed no significant correlation with autoantibodies to acetylcholine nor ryanodine receptors. The DHPR antibody is another marker for thymoma in MG, and it might have some role in clinical symptoms related to E-C coupling.
Sera from patients with myasthenia gravis were examined by Western blot for the presence of antibodies to proteins of the sarcoplasmic reticulum from rabbit skeletal muscle. Fourteen of 30 patients with myasthenia gravis and a thymoma had IgG autoantibodies to the calcium release channel of the sarcoplasmic reticulum (the ryanodine receptor), which plays a crucial role in the mechanism of excitation-contraction coupling in striated muscle. Ryanodine receptor autoantibodies were not detected in any of the 45 sera from patients with myasthenia gravis without a thymoma. Ryanodine receptor autoantibodies may have pathogenetic relevance in thymoma-associated myasthenia gravis.
It is thought that in skeletal muscle excitation-contraction (EC) coupling, the release of Ca2+ from the sarcoplasmic reticulum is controlled by the dihydropyridine (DHP) receptor in the transverse tubular membrane, where it serves as the voltage sensor. We have shown previously that injection of an expression plasmid carrying the skeletal muscle DHP receptor complementary DNA restores EC coupling and L-type calcium current that are missing in skeletal muscle myotubes from mutant mice with muscular dysgenesis. This restored coupling resembles normal skeletal muscle EC coupling, which does not require entry of extracellular Ca2+. By contrast, injection into dysgenic myotubes of an expression plasmid carrying the cardiac DHP receptor cDNA produces L-type calcium current and cardiac-type EC coupling, which does require entry of extracellular Ca2+. To identify the regions responsible for this important functional difference between the two structurally similar DHP receptors, we have expressed various chimaeric DHP receptor cDNAs in dysgenic myotubes. The results obtained indicate that the putative cytoplasmic region between repeats II and III of the skeletal muscle DHP receptor is an important determinant of skeletal-type EC coupling.
An investigation was made into the occurrence of muscular atrophy and muscular pathology in a series of 170 patients with myasthenia gravis. The results can be summarized as follows: (1) Of the 148 patients with generalized myasthenia gravis, 14 showed local muscular atrophies. Of 10 biopsies from atrophic muscles, eight showed neurogenic changes, with or without lymphocytic infiltrations. One biopsy showed lymphocytic infiltrations only, and one showed type II-fibre atrophy (Table 1). No relationship was demonstrable between the presence of clilnical muscular atrophy and age, sex, duration of the disease, severity of the disease, presence of a thymoma, or drug resistant ophthalmoplegia. (2) In this group of patients 61 biopsies were examined from 46 individuals; 40 of these biopsies were taken from the quadriceps muscle. A thymoma was present in 17 patients. Examination disclosed neurogenic changes in 17 biopsies, lymphocytic infiltrates in 21, and myositis in one biopsy (Table 2). A distinct correlation was established between the presence of a thymoma and lymphocytic infiltrates, but none was demonstrable between thymoma and neurogenic changes (Table 3). (3) An enzyme-histochemical study was carried out in 35 cases, including 12 with neurogenic changes. A normal differentiation of type I- and type II-fibres was observed in eight instances, type grouping of type II-fibres in three, and type II-fibre atrophy in two cases. (4) In 21 patients and 19 controls, the smallest mean diameter was determined in the quadriceps muscle. Both type I- and type II-fibres proved to have a smaller mean diameter in the female patients than in the controls. In the male patients this could not be proven. (5) Of the eight patients who had died without disorders of ventilation, 90 muscle specimens were examined postmortem. Four of these patients had a thymoma. Lymphocytic infiltrations, found in 32 biopsy specimens, were mostly observed in the presence of a thymoma. Neurogenic changes were apparently unrelated to the presence of a thymoma (Tables 5 and 6). The post mortem examination included the spinal cord in five, and peripheral nerves in three cases. No abnormalities were found. (6) The muscular atrophy found in patients with myasthenia is not a myopathy but an affection of the lower motor neurone. Neurogenic changes were regularly found in the muscles of patients with myasthenia, even without muscular atrophy. The finding of these changes is no reason to reject the diagnosis. It is postulated that denervation occurs at the neuromuscular junction as a result of permanent absence of acetylcholine.
Structural details of junctional feet in triads of fish muscle are described. These feet have a less dense central core and contact both sarcoplasmic reticulum and T-tubule membranes at tetragonally disposed sites. The distribution of intramembraneous particles differs at the junctional T-membrane, and the junction is asymmetric.
Electrical and mechanical responses to single shocks, slow and fast nerve stimulation (RNS), quantitated EMG, anti-acetylcholine receptor (AChR) and anti-striated muscle (SM) antibodies (ab) were determined in 145 patients with myasthenia gravis (MG). Anti-AChR ab were found in 93% of the myasthenic sera. Decrement of muscle and mechanical responses occurred in 72% and 49%, respectively, the diagnostic yield being positively related to severity of MG. Anti-AChR ab were found in 81% of patients without RNS abnormalities. Decrement at RNS occurred in 33% of the cases without anti-AChR ab compared with 78% of those with elevated titres. Regional curare test (RCT) was diagnostic in 75% of cases with normal RNS. As the combined diagnostic yield of RNS and anti-AChR ab was 96%, RCT and single fibre EMG are rarely indicated. Post-tetanic facilitation and exhaustion, and an abnormal staircase phenomenon occurred in 25%, 44% and 37%, respectively. None of these parameters correlated with severity, type or onset of MG. EMG evidence of myopathy, positively correlated with the presence of anti-SM ab, occurred in 19% of patients examined, 3 times more frequent in those with late onset of MG than in those with early onset; thus myopathy of possible autoimmune origin may coexist with MG. An adequate electrophysiological diagnostic strategy for MG patients is proposed.
The ryanodine receptor (RyR) is one of the key proteins involved in excitation-contraction (E-C) coupling in skeletal muscle, where it functions as a Ca2+ release channel in the sarcoplasmic reticulum (SR) membrane. RyR consists of a single polypeptide of approximately 560 kDa normally arranged in a homotetrameric structure, which contains a carboxyl (C)-terminal transmembrane domain and a large amino (N)-terminal cytoplasmic domain. To test whether the carboxyl-terminal portion of RyR is sufficient to form a Ca2+ release channel, we expressed the full-length (RyR-wt) and C-terminal (RyR-C, approximately 130 kDa) RyR proteins in a Chinese hamster ovary (CHO) cell line, and measured their Ca2+ release channel functions in planar lipid bilayer membranes. The single-channel properties of RyR-wt were found to be similar to those of RyR from skeletal muscle SR. The RyR-C protein forms a cation-selective channel that shares some of the channel properties with RyR-wt, including activation by cytoplasmic Ca2+ and regulation by ryanodine. Unlike RyR-wt, which exhibits a linear current-voltage relationship and inactivates at millimolar Ca2+, the channels formed by RyR-C display significant inward rectification and fail to close at high cytoplasmic Ca2+. Our results show that the C-terminal portion of RyR contains structures sufficient to form a functional Ca2+ release channel, but the N-terminal portion of RyR also affects the ion-conduction and calcium-dependent regulation of the Ca2+ release channel.
Myasthenia gravis (MG) patients with thymoma often have antibodies against the calcium-release channel of the sarcoplasmic reticulum (SR) in striated muscle, the ryanodine receptor (RyR). RyR function can be tested in vitro by measuring the degree of [3H]-ryanodine binding to SR. In this study, sera from 9 out of 14 MG patients containing RyR antibodies inhibited [3H]-ryanodine binding to SR membranes from rat skeletal muscle. The 9 patients with antibodies inhibiting ryanodine binding had more severe MG than those with noninhibiting antibodies (P = 0.006). Sera from MG patients with acetylcholine receptor and titin muscle antibodies but no antibodies against RyR and blood-donor sera did not have an inhibiting effect in the [3H]-ryanodine binding assay. The results show that RyR antibodies in MG patients have high affinity for the RyR, and that the binding of antibodies probably affects calcium release from SR by locking the RyR ion channel in a closed position.
We studied 65 patients with myasthenia gravis (MG). Clinical, neurophysiological, immunological, and histological findings suggested the coexistence of a presumed autoimmune myopathy. The clinical features were persistent pyridostigmine-resistant weakness and atrophy of striated muscles. The myopathy was found more often in patients with late-onset MG than in those with early-onset (37% vs 13%). Patients with myopathy were also prone to have other immune disorders (47% vs 13%). Elevated titres of antibodies against titin were detected more often in patients with electromyography (EMG) evidence of myopathy than in the sera of those without, and only in late-onset MG cases.
This study examined the occlusal state of patients with mandibular prognathism and compared it with that of adults with normal occlusion (controls). It also examined changes in occlusal state after orthognathic operations in these patients. The values of occlusal contact area and bite force in patients before operation were significantly lower than in controls, and occlusal pressure in patients was higher than in controls. The occlusal contact area and bite force of the patients 1 month after the operation had decreased to below preoperative values. These values 12 months after the operation had increased by 2.0 and 1.8 times in women and 1.4 and 1.4 times in men, respectively, compared with preoperative values. However, absolute values remained extremely low compared with those of controls. In contrast to the above, occlusal pressure reached its maximum value 1 month after the operation and at 12 months it was close to the value for controls.
The aim of this study was to evaluate the utility of repetitive nerve stimulation (RNS) of the trigeminal nerve in assessing patients with myasthenia gravis (MG). In 26 normal controls and 21 patients with myasthenia gravis (MG), 2-Hz repetitive stimulation of the trigeminal nerve was performed using a monopolar needle for percutaneous nerve stimulation and recording over the surface of the masseter. In the MG patients, repetitive stimulation of the ulnar, spinal accessory, and facial nerves was also performed. The mean percent decrement in the compound muscle action potential (CMAP) amplitude among the different nerves at rest were: ulnar, 4.3%; spinal accessory, 10.1%; facial, 14%; and trigeminal, 17.3%. The facial nerve demonstrated abnormal decrement in 57% of all patients, compared with the spinal accessory (48%), trigeminal (43%), and ulnar (20%) nerves. All patients tolerated trigeminal RNS better than or as well as facial RNS. The study demonstrates that trigeminal RNS is a safe, reliable, efficient, and well-tolerated technique that provides another cranial nerve-muscle combination that can be used to supplement repetitive stimulation of other limb or cranial nerves in the evaluation of patients with bulbar or generalized MG.
Anti-ryanodine receptor (RyR) antibodies were measured in sera from 33 myasthenia gravis (MG) patients using three peptides from the human RyR1 sequence, two C-terminal peptides included in the functional calcium release channel, and an N-terminal peptide implicated in ion-conduction. Antibodies were more frequently positive against the two C-terminal peptides, particularly in thymoma-associated MG. In a preliminary open trial with FK506, immunosuppressant and enhancer of RyR-related sarcoplasmic calcium release, the authors observed the sustained benefits in anti-RyR-positive MG patients.
Muscle-specific tyrosine kinase (MuSK) antibodies are found in some patients with "seronegative" myasthenia gravis (MG), but how they cause myasthenic symptoms is not clear. We visualized acetylcholine receptors (AChRs) and complement component 3 (C3) in muscle biopsies from 10 Japanese MG patients with MuSK antibodies, compared with 42 with AChR antibodies. The AChR density was not significantly decreased in MuSK antibody (Ab)-positive end-plates compared with AChR antibody-positive end-plates, and C3 was detected in only two of eight MuSK Ab-positive patients. MuSK antibodies do not appear to cause substantial AChR loss, complement deposition, or morphological damage. Effects on MuSK function need to be explored.
Nineteen healthy volunteers (median age, 25; range, 18-51 years) were enrolled in a study to obtain normative values for stimulated jitter in the masseter muscle. Axonal microstimulation was performed via a monopolar needle electrode introduced in the masseter 2-2.5 cm above the mandibular angle on the line connecting it with the lateral canthus. The recording single-fiber electromyography (SFEMG) electrode was inserted anteriorly in the twitching area of the muscle. The mean consecutive difference (MCD) values for the 426 endplates studied followed a distribution skewed to the left, with a minimum value of 4.3 micros, maximal 44.7 micros, and a maximum of distribution at 11 micros. Mean pooled MCD measured 16.0 micros, and the mean of mean MCD per study was 13.6 micros. The value of the 95th upper percentile for an individual fiber was 29.3 micros. We suggest an upper normal limit for mean MCD per study of 21 micros and upper normal limit of MCD for individual fibers of 30 micros. The stimulated jitter study of masseter muscle is easy and reliable.
To investigate whether excitation-contraction (E-C) coupling of muscle is impaired in patients with myasthenia gravis (MG).
In 51 patients with generalized MG and 35 normal subjects, compound muscle action potentials (CMAPs) of the abductor pollicis brevis, and movement-related potentials using an accelerometer placed at the thumb tip were simultaneously recorded after median nerve stimulation at the wrist. The E-C coupling time (ECCT) was estimated by a latency difference between CMAP and movement-related potential. Antibodies against acetylcholine receptor (AChR), ryanodine receptor (RyR), and muscle specific receptor tyrosine kinase (MuSK) were measured by immunoassays.
The mean ECCT was significantly longer in patients with MG (mean+/-SEM; 2.79+/-0.1 ms; p=0.002) than in normal controls (2.52+/-0.1 ms). Among MG patients, the mean ECCT was longer for patients with thymoma than for those without it (P=0.04), and was shorter for patients treated with FK506 (an immunosuppressant and also an enhancer of RyR related Ca(2+) release) than for those not receiving this treatment (p=0.04). ECCT had no significant correlation with anti-AChR, anti-RyR, or anti-MuSK antibodies.
In MG, E-C coupling appears to be impaired, particularly in patients with thymoma, and FK506 possibly facilitates E-C coupling.
The functional implication of impaired E-C coupling is not established, but it may contribute to muscle weakness in patients with MG.
Myasthenia gravis (MG) is an autoimmune disease caused in 85% of the patients by acetylcholine receptor (AChR) antibodies. Non-AChR muscle antibodies, against titin and ryanodine receptor (RyR) are mainly found in sera of patients with thymoma or late-onset MG. The occurrence of RyR antibodies increases the risk for severe MG and should lead to active immunomodulating treatment already at MG onset. The aim in this study was to describe the association between symptoms at MG onset and antibody profile in 152 patients. Patients with RyR antibodies had the highest rate of bulbar, respiratory and neck involvement at MG onset. They also had the highest frequency of non-limb MG symptoms. Neck weakness occurred in 40%. Respiratory difficulties at MG onset occurred in patients with titin antibodies, with and without RyR antibodies. Patients with RyR antibodies have a distinctive non-limb MG symptom profile, with bulbar, ocular, neck, and respiratory symptoms. These features, identified as early as at the first examination by a neurologist, characterize the RyR antibody positive subgroup at MG onset.
Comparison of ECCT in anti-RyR-positive and -negative MG patients. Closed circle and bar indicate mean and SD in each group Functional calcium release channel formed by the carboxyl-terminal portion of ryanodine receptor
- Mann
- Whitney
- Bhat Mb
- J Zhao
- H Takeshima
- Ma
Comparison of ECCT in anti-RyR-positive and -negative MG patients. Closed circle and bar indicate mean and SD in each group. p = 0.017, by Mann–Whitney U-test. References Bhat MB, Zhao J, Takeshima H, Ma J. Functional calcium release channel formed by the carboxyl-terminal portion of ryanodine receptor. Biophys J 1997;73:1329–36.
Measurement of excitation–contraction coupling time of masseter in lower jaw movement. In: The XVIth international SFEMG and QEMG course and the IXth QEMG conference proceedings Anti-ryanodine receptor–positive acetylcholine receptor–negative myasthenia gravis: evidence of impaired E–C coupling
- T Imai
- E Tsuda
- T Hozuki
- S Hisahara
- M Nonaka
- Shimohama
- T Imai
- E Tsuda
- T Toyoshima
- H Yoshikawa
- M Motomura
- Shimohama
Imai T, Tsuda E, Hozuki T, Hisahara S, Nonaka M, Shimohama S. Measurement of excitation–contraction coupling time of masseter in lower jaw movement. In: The XVIth international SFEMG and QEMG course and the IXth QEMG conference proceedings; 2007. p. 187. Imai T, Tsuda E, Toyoshima T, Yoshikawa H, Motomura M, Shimohama S. Anti-ryanodine receptor–positive acetylcholine receptor–negative myasthenia gravis: evidence of impaired E–C coupling. Muscle Nerve 2011;43:294–5.
Measurement of excitation-contraction coupling time of masseter in lower jaw movement. In: The XVIth international SFEMG and QEMG course and the IXth QEMG conference proceedings
- T Imai
- E Tsuda
- T Hozuki
- S Hisahara
- M Nonaka
- S Shimohama