We hypothesized that metabolic adaptations to muscle inactivity are most pronounced when neurotrophic influence is disrupted. In rat diaphragm muscle (Dia(m)), 2 wk of unilateral denervation or tetrodotoxin nerve blockade resulted in a reduction in succinate dehydrogenase (SDH) activity of type I, IIa, and IIx fibers (~50, 70, and 24%, respectively) and a decrease in SDH variability among fibers (~63%). In contrast, inactivity induced by spinal cord hemisection at C2 (ST) resulted in much less change in SDH activity of type I and IIa fibers (~27 and 24%, respectively) and only an ~30% reduction in SDH variability among fibers. Actomyosin adenosinetriphosphatase (ATPase) activities of type I, IIx, and IIb fibers in denervated and tetrodotoxin-treated Dia(m) were reduced by ~20, 45, and 60%, respectively, and actomyosin ATPase variability among fibers was ~60% lower. In contrast, only actomyosin ATPase activity of type IIb fibers was reduced (~20%) in ST Dia(m). These results suggest that disruption of neurotrophic influence has a greater impact on muscle fiber metabolic properties than inactivity per se.
- actomyosin adenosinetriphosphatase activity
- muscle fiber
- spinal hemisection
- succinate dehydrogenase activity
ASJC Scopus subject areas
- Physiology (medical)