Meeting Abstract
Hibernating mammals can resist muscle atrophy despite months of inactivity by lowering their body temperature and activating novel physiological pathways. However, since they employ both strategies simultaneously, the effects of the two mechanisms cannot be separated. In this study, we use the western fence lizard, Sceloporus occidentalis, as an ectothermic model to determine whether a reduction in metabolic rate is sufficient to resist muscle atrophy. To induce atrophy, we severed the sciatic nerve to prevent contraction of the gastrocnemius muscle and housed experimental and control lizards at either 15° or 30°C for 6-7 weeks on a 12/12 light/dark cycle. After treatment, we dissected out the muscles and used muscle ergometry to measure maximum isometric force (P0), the force-velocity relationship, and contractile dynamics. We weighed and fixed the muscles at their optimal length for morphological measurements, and flash froze a subset, which we stained for NADH and ATPase to characterize fiber types. At 30°C, denervated muscles have a 20% reduction in muscle mass and a 12% reduction in P0, but no differences were seen at 15°C. In both treatments, no differences were detected between groups in muscle stress, shortening velocity or most contractile parameters. Although muscle atrophy in mammals is often associated with a shift from slow to fast fiber types, we found no difference in the percentage of SO, FG, or FOG fibers between treatment groups. We conclude that low metabolic rate is sufficient to prevent muscle atrophy in western fence lizards, and that atrophy in the lizard gastrocnemius is not associated with a change in fiber type composition or contractile dynamics. This work suggests that ectothermic vertebrates may have an intrinsic mechanism to resist muscle atrophy during seasonal periods of inactivity.
