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Experimental design. (A) Leg anatomy of the western fence lizard. An incision was made on the dorsal proximal thigh and the sciatic nerve was severed to denervate the medial gastrocnemius muscle. (B) Representative time series traces showing force (relative to maximum force, F max ) and length during two isotonic contractions at 30% and 70% of maximum contractile force (P 0 ). Gray vertical bars indicate the time at which force and velocity measurements were taken for each contraction. (C) Force–velocity relationship for a representative muscle characterized using a series of isotonic contractions between 5% and 100% of P 0. The contractions shown in B are indicated with large circles. The force–velocity data were fitted with a hyperbolic–linear equation (Marsh and Bennett, 1986). L f , fiber length.
Source publication
Extended periods of skeletal muscle disuse can cause a significant loss of contractile proteins, which compromises the ability to generate force, mechanical work or power, thus compromising locomotor performance. Several hibernating organisms can resist muscle atrophy despite months of inactivity. This resistance has been attributed to a reduction...
Contexts in source publication
Context 1
... and toe-pinch reflexes were no longer present. A small dorsal incision was made on the posterior portion of hindlimb (where the thigh meets the trunk). Ceramic-coated forceps were then inserted in between the iliofibularis and ilioischiotibialis muscles to grasp the sciatic nerve, which was isolated and pulled free from the surrounding structures (Fig. 1A). A section of the sciatic nerve no less than 2 mm in length was then removed to prevent regrowth of the nerve within the 6 week experimental period. Sham surgeries were performed on control limbs following the same procedure as the denervated group but without extracting and cutting the sciatic nerve. Sutures (6-0 silk) were used to ...
Context 2
... a stimulation pulse duration of 0.2 ms and a frequency of 80 pulses s -1 for 400 ms. A tetanic contraction starting at the optimal length of the twitch force-length curve (L 0 ) was used to determine maximum isometric force (P 0 ). A series of isotonic tetanic contractions was used to characterize the force-velocity relationship of each muscle (Fig. 1B). After force developed to a preset value, it was maintained by the servomotor and the muscles shortened. Force-velocity curves were characterized for each muscle from 7-10 isotonic contractions ranging from 5% to 90% of P 0 . We elicited an isometric contraction in the middle and at the end of each experiment to ensure no drop in P 0 . ...
Context 3
... obtained velocity measurements from each contraction by calculating the average change in muscle length divided by the duration of the constant velocity portion of muscle shortening. Force measurements were taken as the average force for the period of time over which velocity measurements were taken (Fig. 1B). To characterize the force-velocity properties of the gastrocnemius, we plotted force and the corresponding shortening velocity and fitted An incision was made on the dorsal proximal thigh and the sciatic nerve was severed to denervate the medial gastrocnemius muscle. (B) Representative time series traces showing force (relative to ...
Citations
... Specifically, it has been reported that cardiovascular functions are dramatically suppressed in hibernating ectotherms [9], although heart continues to work at a low rate under cold conditions. Skeletal muscle remains largely immobile during hibernation, but must resume full function upon arousal from torpor [10]. Indeed, a growing number of studies have confirmed that muscle atrophy does not occur in hibernating animals [11,12]. ...
Background
In response to seasonal cold and food shortage, the Xizang plateau frogs, Nanorana parkeri (Anura: Dicroglossidae), enter a reversible hypometabolic state where heart rate and oxygen consumption in skeletal muscle are strongly suppressed. However, the effect of winter hibernation on gene expression and metabolic profiling in these two tissues remains unknown. In the present study, we conducted transcriptomic and metabolomic analyses of heart and skeletal muscle from summer- and winter-collected N. parkeri to explore mechanisms involved in seasonal hibernation.
Results
We identified 2407 differentially expressed genes (DEGs) in heart and 2938 DEGs in skeletal muscle. Enrichment analysis showed that shared DEGs in both tissues were enriched mainly in translation and metabolic processes. Of these, the expression of genes functionally categorized as “response to stress”, “defense mechanisms”, or “muscle contraction” were particularly associated with hibernation. Metabolomic analysis identified 24 and 22 differentially expressed metabolites (DEMs) in myocardium and skeletal muscle, respectively. In particular, pathway analysis showed that DEMs in myocardium were involved in the pentose phosphate pathway, glycerolipid metabolism, pyruvate metabolism, citrate cycle (TCA cycle), and glycolysis/gluconeogenesis. By contrast, DEMs in skeletal muscle were mainly involved in amino acid metabolism.
Conclusions
In summary, natural adaptations of myocardium and skeletal muscle in hibernating N. parkeri involved transcriptional alterations in translation, stress response, protective mechanisms, and muscle contraction processes as well as metabolic remodeling. This study provides new insights into the transcriptional and metabolic adjustments that aid winter survival of high-altitude frogs N. parkeri.
