Abstract
Previous studies indicate that hibernating animals, under conditions of torpor for long periods, show an increased oxidative muscle fibers (type I) ratio and a decreased glycolytic muscle fibers (type II) ratio in skeletal muscle and accompanied by extraordinary oxidative ability. This observation is completely contrasted with non-hibernators, which show a shift of oxidative muscle fibers (type I) to glycolytic muscle fibers (type II). Presently, the mechanisms by which these changes occur remain unclear. To investigate the mechanism of high oxidative capacity of the skeletal muscles in hibernating ground squirrels, capillary density (CD), and capillary/fiber (C/F) were measured by immunohistochemistry. mRNA expression levels of hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) were determined using real-time quantitative PCR assay. Spectrophotometry was applied to determine the activities of hexokinase (PK), pyruvate kinase (HK), and cytochrome c oxidase (CcO). Inthe soleus muscle (SOL), mRNA expression levels of HIF-1αandVEGF in torpor became slightly lower but were not statistically significant; they were, however, significantly higher in the arousal group. In hibernating animals, no significant change occurred in CD but C/F increased by 15 %. CcO showed the highest activity in torpor. There were no significant differences in the activities of HK and PK between the torpid animals and summer active animals in SOL. However, PK activity increased by 34 % after hibernation. Oxidative capacitymay be ensured by an increase of capillary supply of skeletal muscle in hibernating animals.
Highlights
Previous studies indicate that hibernating animals, under conditions of torpor for long periods, show an increased oxidative muscle fibers ratio and a decreased glycolytic muscle fibers ratio in skeletal muscle and accompanied by extraordinary oxidative ability
Fibers of type I mainly rely on aerobic metabolism while fibers of type II mainly rely on anaerobic metabolism
Compared with the pre-hibernation group (Pre-H) group, expression levels of HIF-α1 and vascular endothelial growth factor (VEGF) mRNA decreased in the hibernating group, albeit not significantly (P > 0.05)
Summary
Previous studies indicate that hibernating animals, under conditions of torpor for long periods, show an increased oxidative muscle fibers (type I) ratio and a decreased glycolytic muscle fibers (type II) ratio in skeletal muscle and accompanied by extraordinary oxidative ability. This observation is completely contrasted with non-hibernators, which show a shift of oxidative muscle fibers (type I) to glycolytic muscle fibers (type II). The transformation of muscle fiber from type I to type II, corresponding with a reduced oxidative capacity, is one of the mechanisms that have been identified to contribute to muscle atrophy in simulated microgravity (using hindlimb-unloading in animals or in bed rested subjects) as well as in spaceflight (Bricout et al 1999). Inadequate oxygen supply, which occurred in skeletal muscle induced by the cephalad blood redistribution in these models (McDonald et al 1992; Yamasaki et al 2004) may play an important role in this transformation
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
