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Protein expressions of (Thr 287 )p-CaMKII and SKca2.2 before and after treatment with KN-92 and KN-93 in neonatal rat atrial myocytes. (A) Effects of KN-92 and KN-93 on the expression of (Thr 287 )p-CaMKII in neonatal rat atrial myocytes (n=4). (B) Effects of KN-92 and KN-93 on the expression of SK2 protein. * P<0.05 vs. KN92.
Source publication
Background
Increased small-conductance Ca²⁺-activated K⁺ current (SK), abnormal intracellular Ca²⁺ handling, and enhanced expression and activity of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) have been found in clinical and/or experimental models of atrial fibrillation (AF), but the cumulative effect of these phenomena and their mechanism...
Contexts in source publication
Context 1
... further confirm the effect of CaMKII phosphorylation on SK2 channel activation in AF, we evaluated the effect of (Thr 287 )p- CaMKII on SK2 channel protein expression. Figure 8A shows that treatment with KN-92 (1 µmol/l, n=4) did not affect the ex- pression of (Thr 287 )p-CaMKII expression, while KN-93 (1 µmol/l, n=4) significantly decreased the expression of (Thr 287 )p-CaMKII in the neonatal rat atrial myocytes (P<0.05). As expected, KN- 93 significantly decreased the protein expression of SK2 chan- nels in neonatal rat atrial myocytes (n=4, P<0.05) ( Figure 8B). ...
Context 2
... 8A shows that treatment with KN-92 (1 µmol/l, n=4) did not affect the ex- pression of (Thr 287 )p-CaMKII expression, while KN-93 (1 µmol/l, n=4) significantly decreased the expression of (Thr 287 )p-CaMKII in the neonatal rat atrial myocytes (P<0.05). As expected, KN- 93 significantly decreased the protein expression of SK2 chan- nels in neonatal rat atrial myocytes (n=4, P<0.05) ( Figure 8B). ...
Citations
... Our default cAF model does not account for any AF-associated SK channel remodeling. However, we performed a separate set of simulations in which both SK channel conductance and Ca 2+sensitivity are altered as seen in AF (29,47). ...
... The degree of AF-induced remodeling has also been shown to impact ISK function, whereby studies in dog and human have shown that SK channel expression is reduced in cAF (23,(63)(64)(65), and ISK block does not affect the APD. Other studies have instead reported increased ISK in cAF (29,47,66). In our recent investigation, we did not find changes in SK channel expression at mRNA or protein level, but we demonstrated that ISK is significantly increased in human cAF vs. nSR, due to enhanced Ca 2+ -dependent SK channel gating and membrane trafficking and targeting (29). ...
... In our cAF simulations, we also assumed unchanged Ca 2+ -dependent activation of ISK compared to nSR. Experiments in atrial cardiomyocytes from patients have shown increased affinity for intracellular Ca 2+ in cAF vs. nSR (47), which could contribute to ISK upregulation in disease (29). Increasing Ca 2+ affinity minimally impacts the results produced with the Grandi et al. model, especially in terms of regulation of APD, ERP, and CaT (Fig. S3A). ...
By sensing changes in intracellular Ca2+, small-conductance Ca2+-activated K+ (SK) channels dynamically regulate the dynamics of the cardiac action potential (AP) on a beat-to-beat basis. Given their predominance in atria vs. ventricles, SK channels are considered a promising atrial-selective pharmacological target against atrial fibrillation (AF), the most common cardiac arrhythmia. However, the precise contribution of SK current (ISK) to atrial arrhythmogenesis is poorly understood, and may potentially involve different mechanisms that depend on species, heart rates, and degree of AF-induced atrial remodeling. Both reduced and enhanced ISK have been linked to AF. Similarly, both SK channel up- and downregulation have been reported in chronic AF (cAF) vs. normal sinus rhythm (nSR) patient samples. Here, we use our multi-scale modeling framework to obtain mechanistic insights into the contribution of ISK in human atrial myocyte electrophysiology. We simulate several protocols to quantify how ISK modulation affects the regulation of AP duration (APD), Ca2+ transient, refractoriness, and occurrence of alternans and delayed afterdepolarizations (DADs). Our simulations show that ISK activation shortens the APD and atrial effective refractory period, limits Ca2+ cycling, and slightly increases the propensity for alternans in both nSR and cAF conditions. We also show that increasing ISK counteracts DAD development by reducing the coupling between transmembrane potential and intracellular Ca2+. Taken together, our results suggest that increasing ISK in human atrial myocytes could promote reentry, while protecting against triggered activity. Depending on the leading arrhythmogenic mechanism, ISK inhibition may thus be a beneficial or detrimental anti-AF strategy.
... I SK participates in AP termination, shortening APD and ERP, changes likely to promote AP re-entry. Atrial myocytes from patients in rapid AF showed increased I SK attributed to intracellular Ca 2+ overload [115,116]. SK channel inhibition might then offer a potential therapeutic target for AF by prolonging atrial ERP without affecting QT intervals [24,[117][118][119]. ...
Ca ²⁺ -activated K ⁺ channels are critical to cellular Ca ²⁺ homeostasis and excitability; they couple intracellular Ca ²⁺ and membrane voltage change. Of these, the small, 4–14 pS, conductance SK channels include three, KCNN1-3 encoded, SK1/KCa2.1, SK2/KCa2.2 and SK3/KCa2.3, channel subtypes with characteristic, EC 50 ∼ 10 nM, 40 pM, 1 nM, apamin sensitivities. All SK channels, particularly SK2 channels, are expressed in atrial, ventricular and conducting system cardiomyocytes. Pharmacological and genetic modification results have suggested that SK channel block or knockout prolonged action potential durations (APDs) and effective refractory periods (ERPs) particularly in atrial, but also in ventricular, and sinoatrial, atrioventricular node and Purkinje myocytes, correspondingly affect arrhythmic tendency. Additionally, mitochondrial SK channels may decrease mitochondrial Ca ²⁺ overload and reactive oxygen species generation. SK channels show low voltage but marked Ca ²⁺ dependences (EC 50 ∼ 300–500 nM) reflecting their α-subunit calmodulin (CaM) binding domains, through which they may be activated by voltage-gated or ryanodine-receptor Ca ²⁺ channel activity. SK function also depends upon complex trafficking and expression processes and associations with other ion channels or subunits from different SK subtypes. Atrial and ventricular clinical arrhythmogenesis may follow both increased or decreased SK expression through decreased or increased APD correspondingly accelerating and stabilizing re-entrant rotors or increasing incidences of triggered activity.
This article is part of the theme issue ‘The heartbeat: its molecular basis and physiological mechanisms’.
... SK channels were first identified in the heart in 2003 [14,15], and their distribution and functions in heart tissue have since been extensively studied [16][17][18]. SK channels have been found in both atrial and ventricular tissues in animals and humans [7,12,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. In mouse atrial and ventricular myocytes, quantification of SK1 and SK3 transcripts showed a higher level of SK1 expression in atria versus ventricles, while SK3 is expressed at a simar level in atria and ventricles [12]. ...
... Likewise, Qi et al. reported upregulation of SK1 and SK2 protein induced by atrial tachypacing in dog PVs and left atrial cells; SK2 mRNA expression was also increased, although no significant changes in SK1 mRNA were observed, suggesting that overexpression of SK1 may be the result of posttranslational CaMKII, which is required for SK channel calcium-dependent activation. CaMKII exhibited significantly increased expression alongside, increased intracellular calcium levels in human AF tissue studied by Fan et al. [32]. ...
... It is also possible that SK channels are initially upregulated in AF before being downregulated due to atrial remodeling. There are several reported mechanisms by which SK channels are regulated in AF, including histone deacetylase related epigenetic mechanisms [95], miRNA [26], and CaMKII [32]. ...
Extensive evidence indicates that small-conductance Ca2+-activated K+ channels (SK channels) help regulate cardiac rhythm and myocardial function in physiological and pathophysiological conditions. This chapter will begin by discussing the basic physiology of SK channel expression, localization, and activation under normal conditions, before proceeding to address the impact of SK channel dysfunction on a variety of cardiac pathologies including atrial fibrillation (AF), ventricular arrhythmias (VA), cardiac hypertrophy/heart failure (HF) and myocardial ischemia/reperfusion (IR) injury. The critical role of aberrant SK channel regulation will also be discussed to establish unifying mechanisms of SK channel pathology across these different conditions. Several animal model and human tissue experiments suggest that pharmacologic modulation of SK channel function may be beneficial in controlling AF, VA, cardiomyopathy and myocardial IR injury. Therefore, targeting SK channels may represent a promising new therapeutic avenue for treating a variety of cardiovascular disease states.
... KCNN1 is expressed in human and murine heart with atrial predominance (Tuteja et al., 2005;Xu et al., 2003), indicating a potential advantage for K Ca 2.1 channels as atrial-selective targets in AF therapy (Hancox et al., 2016). In patients with cAF and preserved LVEF, expression of K Ca 2.1 (KCNN1) was reduced compared to sinus rhythm (SR) subjects (Fan et al., 2018;Yu et al., 2012). At the functional level, K Ca channels underlie the cardiac I K,Ca current and are inhibited by apamin (Zhang, Wu, et al., 2014) with different affinity (K Ca 2.2>K Ca 2.3>K Ca 2.1 [Lamy et al., 2010]). ...
Atrial fibrillation (AF) with concomitant heart failure (HF) poses a significant therapeutic challenge. Mechanism-based approaches may optimize AF therapy. Small-conductance, calcium-activated K+ (KCa , KCNN) channels contribute to cardiac action potential repolarization. KCNN1 exhibits predominant atrial expression and is downregulated in chronic AF patients with preserved cardiac function. Epigenetic regulation is suggested by AF suppression following histone deacetylase (HDAC) inhibition. We hypothesized that HDAC-dependent KCNN1 remodeling contributes to arrhythmogenesis in AF complicated by HF. The aim of this study was to assess KCNN1 and HDAC1-7 and 9 transcript levels in AF/HF patients and in a pig model of atrial tachypacing-induced AF with reduced left ventricular function. In HL-1 atrial myocytes, tachypacing and anti-Hdac siRNAs were employed to investigate effects on Kcnn1 mRNA levels. KCNN1 expression displayed side-specific remodeling in AF/HF patients with upregulation in left and suppression in right atrium. In pigs, KCNN1 remodeling showed intermediate phenotypes. HDAC levels were differentially altered in humans and pigs, reflecting highly variable epigenetic regulation. Tachypacing recapitulated downregulation of Hdacs 1, 3, 4, 6, and 7 with a tendency towards reduced Kcnn1 levels in vitro, indicating that atrial high rates induce remodeling. Finally, Kcnn1 expression was decreased by knockdown of Hdacs 2, 3, 6, and 7 and enhanced by genetic Hdac9 inactivation, while anti-Hdac 1, 4, and 5 siRNAs did not affect Kcnn1 transcript levels. In conclusion, KCNN1 and HDAC expression is differentially remodeled in AF complicated by HF. Direct regulation of KCNN1 by HDACs in atrial myocytes provides a basis for mechanism-based antiarrhythmic therapy.
... 12 Furthermore, reduced expression of K Ca 2.1, K Ca 2.2, and K Ca 2.3 has been detected in patients with persistent or permanent AF and preserved cardiac function when compared to sinus rhythm (SR) subjects. 7,8,13 Of note, either inappropriate shortening or excessive prolongation of atrial APD may increase AF susceptibility. 3,11,14,15 Thus, the therapeutic efficacy of interventions targeting K Ca 2 channels will depend on the functional K Ca 2 homeostasis, which is affected by individual patient characteristics and by environmental factors that determine specific K Ca 2 channel remodeling. ...
... Reduced expression of K Ca 2.1, K Ca 2.2, and K Ca 2.3 in patients with preserved cardiac function and persistent or permanent AF has previously been reported. 7,8,13 The present work extends AF-related K Ca 2 downregulation to patients with severely impaired left ventricular function, highlighting a broader mechanism of atrial electrophysiological remodeling. While these results suggest uniform K Ca 2 remodeling during AF, a more complex picture with species-and mechanism-based remodeling of the channels is supported by data obtained from a canine model of AF induced by 7 days atrial tachypacing. ...
Aim
Effective antiarrhythmic treatment of atrial fibrillation (AF) constitutes a major challenge, in particular, when concomitant heart failure (HF) is present. HF-associated atrial arrhythmogenesis is distinctly characterized by prolonged atrial refractoriness. Small-conductance, calcium-activated K⁺ (KCa, SK, KCNN) channels contribute to cardiac action potential repolarization and are implicated in AF susceptibility and therapy. The mechanistic impact of AF/HF-related triggers on atrial KCa channels is not known. We hypothesized that tachycardia, stretch, β-adrenergic stimulation, and hypoxia differentially determine KCa2.1–2.3 channel remodeling in atrial cells.
Methods
KCNN1-3 transcript levels were assessed in AF/HF patients and in a pig model of atrial tachypacing-induced AF with reduced left ventricular function. HL-1 atrial myocytes were subjected to proarrhythmic triggers to investigate the effects on Kcnn mRNA and KCa channel protein.
Results
Atrial KCNN1-3 expression was reduced in AF/HF patients. KCNN2 and KCNN3 suppression was recapitulated in the corresponding pig model. In contrast to human AF, KCNN1 remained unchanged in pigs. Channel- and stressor-specific remodeling was revealed in vitro. Lower expression levels of KCNN1/KCa2.1 were linked to stretch and β-adrenergic stimulation. Furthermore, KCNN3/KCa2.3 expression was suppressed upon tachypacing and hypoxia. Finally, KCNN2/KCa2.2 abundance was specifically enhanced by hypoxia.
Conclusion
Reduction of KCa2.1–2.3 channel expression might contribute to the action potential prolongation in AF complicated by HF. Subtype-specific KCa2 channel remodeling induced by tachypacing, stretch, β-adrenergic stimulation, or hypoxia is expected to differentially determine atrial remodeling, depending on patient-specific activation of each triggering factor. Stressor-dependent KCa2 regulation in atrial myocytes provides a starting point for mechanism-based antiarrhythmic therapy.
... CaMKII has also been shown to autophosphorylate independently of Epac2 in atrial appendage samples of AF patients. Thus, CaMKII autophosphorylation increased Ca 2+ sensitivity of apamin sensitive small-conductance Ca 2+ -activated K + current (I KAS ) in AF [90]. ...
... Thus, contrary to what happens with contraction, the PDE3 or PDE4 control on propensity of 5-HT-evoked arrhythmias on human atrial trabeculae from patients in sinus rhythm or with paroxysmal AF, is lost in persistent AF [93]. 5-HT stimulation has been shown to increase I f [94] and I Ca,L [91,94] in HAMs, but less than β-adrenergic stimulation [91,95] and without regulation of PDE3 or PDE4 [90]. ...
Atrial fibrillation (AF) is the most common cardiac arrhythmia, largely associated to morbidity and mortality. Over the past decades, research in appearance and progression of this arrhythmia have turned into significant advances in its management. However, the incidence of AF continues to increase with the aging of the population and many important fundamental and translational underlaying mechanisms remain elusive. Here, we review recent advances in molecular and cellular basis for AF initiation, maintenance and progression. We first provide an overview of the basic molecular and electrophysiological mechanisms that lead and characterize AF. Next, we discuss the upstream regulatory factors conducting the underlying mechanisms which drive electrical and structural AF-associated remodeling, including genetic factors (risk variants associated to AF as transcriptional regulators and genetic changes associated to AF), neurohormonal regulation (i.e., cAMP) and oxidative stress imbalance (cGMP and mitochondrial dysfunction). Finally, we discuss the potential therapeutic implications of those findings, the knowledge gaps and consider future approaches to improve clinical management.
... In contrast, PKA phosphorylation at serine-465 of SK2 channel attenuates rectification of SK currents by reducing the voltage-dependent inhibition by intracellular Ca 2+ , leading to the upregulation of SK currents in ventricular myocytes from hypertrophic hearts [37]. In human AF, autophosphorylated CaMKII at Thr287 is significantly increased, leading to the upregulated SK currents in atria with increased Ca 2+ sensitivity but decreased expression of SK1, SK2, and SK3 channels [30]. ...
Small-conductance Ca²⁺-activated K⁺ (SK, KCa2) channels are encoded by KCNN genes, including KCNN1, 2, and 3. The channels play critical roles in the regulation of cardiac excitability and are gated solely by beat-to-beat changes in intracellular Ca²⁺. The family of SK channels consists of three members with differential sensitivity to apamin. All three isoforms are expressed in human hearts. Studies over the past two decades have provided evidence to substantiate the pivotal roles of SK channels, not only in healthy heart but also with diseases including atrial fibrillation (AF), ventricular arrhythmia, and heart failure (HF). SK channels are prominently expressed in atrial myocytes and pacemaking cells, compared to ventricular cells. However, the channels are significantly upregulated in ventricular myocytes in HF and pulmonary veins in AF models. Interests in cardiac SK channels are further fueled by recent studies suggesting the possible roles of SK channels in human AF. Therefore, SK channel may represent a novel therapeutic target for atrial arrhythmias. Furthermore, SK channel function is significantly altered by human calmodulin (CaM) mutations, linked to life-threatening arrhythmia syndromes. The current review will summarize recent progress in our understanding of cardiac SK channels and the roles of SK channels in the heart in health and disease.
... In a rabbit model of short-term atrial burst pacing, SK2 mRNA, protein, and corresponding I KAS were increased in the pulmonary veins, involving in the early electrical remodeling [68]. In contrast, mRNA and proteins of SK channels were downregulated in patients with chronic AF, suggesting an opposite regulatory direction in the chronic remodeling process [27,51,81,108]. In streptozotocin-induced type 1 diabetic mice, the expression of both SK2 and SK3 was reduced in atrium [101]. However, SK2 expression in atria was downregulated, whereas SK3 was upregulated in a type 2 diabetic mouse model [53]. ...
... However, SK2 expression in atria was downregulated, whereas SK3 was upregulated in a type 2 diabetic mouse model [53]. While the downregulation of SK channels led to decreased I KAS in most AF studies [51,81,108], intriguingly increase of I KAS could be possible via the enhanced Ca 2+ and Ca 2+ -SK interaction [27]. On the other hand, upregulation of SK channel expression was commonly observed in HF. ...
... I KAS was increased via the Ca 2+ /calmodulin-dependent protein kinase II (CaMKII)-dependent pathway in hypertrophic ventricles in rats [61]. Similarly in AF patients, CaMKII activation by autophosphorylation at Thr287 increased calcium sensitivity of I KAS and consequently induced increased I KAS [27]. ...
Apamin-sensitive small-conductance calcium-activated potassium (SK) current (IKAS) plays an important role in cardiac repolarization under a variety of physiological and pathological conditions. The regulation of cardiac IKAS relies on SK channel expression, intracellular Ca2+, and interaction between SK channel and intracellular Ca2+. IKAS activation participates in multiple types of arrhythmias, including atrial fibrillation, ventricular tachyarrhythmias, and automaticity and conduction abnormality. Recently, sex dimorphisms in autonomic control have been noticed in IKAS activation, resulting in sex-differentiated action potential morphology and arrhythmogenesis. This review provides an update on the Ca2+-dependent regulation of cardiac IKAS and the role of IKAS on arrhythmias, with a special focus on sex differences in IKAS activation. We propose that sex dimorphism in autonomic control of IKAS may play a role in J wave syndrome.
... Recently, Fan et al. [47] reported the findings that SK currents were increased but the mRNA and protein expressions of SK channel were decreased in patients with AF. This contradictory phenomenon was mainly due to Ca 21 / calmodulin-dependent protein kinase II activation by autophosphorylation at Thr287, which increased the calcium sensitivity of SK channels and induced increased SK currents in AF patients. ...
Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia in the world. Although much technological progress in the treatment of AF has been made, there is an urgent need for better treatment of AF due to its high rates of morbidity and mortality. The anti-arrhythmic drugs currently approved for marketing have significant limitations and side effects such as life-threatening ventricular arrhythmias and hypotension. The small conductance Ca²⁺-activated K⁺ channels (SK channels) are dependent on intracellular Ca²⁺ concentrations, which tightly integrate with membrane potential. Given the predominant expression in the atria of many species, including humans, they are now emerging as a therapeutic target for treating AF. This review aimed to illustrate the characteristics and function of SK channels. Moreover, it discussed the regulation of SK channels and their potential as a therapeutic target of AF.
... Li et al. (2011) showed that SK2 current density is bigger in atrial cells from patients diagnosed with persistent AF (at least 6 months) than in non-AF patients. At a molecular level, CAMKII levels are increased in human AF atrial cells, associated with a left shift of the SK calcium dose-response curve and bigger currents (Fan et al., 2018). Oppositely, in atrial biopsies from chronic AF patients (more than 6 months preceding a medical surgery), the SK1, SK2, (Yu et al., 2012) or SK3 (Skibsbye et al., 2014) transcripts and protein levels are reduced compared with atrial biopsies obtained from patients with sinus rhythm. ...
Calcium-activated potassium channels are a heterogeneous family of channels that, despite their different biophysical characteristics, structures, and pharmacological signatures, play a role of transducer between the ubiquitous intracellular calcium signaling and the electric variations of the membrane. Although this family of channels was extensively described in various excitable and non-excitable tissues, an increasing amount of evidences shows their functional role in the heart. This review aims to focus on the physiological role and the contribution of the small and intermediate calcium-activated potassium channels in cardiac pathologies.
