Metabolic and phenotypic adaptations of diaphragm muscle fibers
with inactivation.
Zhan, Wen-Zhi, Hirofumi Miyata, Y. S. Prakash, and Gary C. Sieck.
Departments of Anesthesiology, and Physiology & Biophysics,
Mayo Foundation, Rochester, MN 55905
APStracts 3:0548A, 1996.
We hypothesized that metabolic adaptations to muscle inactivity are
most pronounced when neurotrophic influence is disrupted. In rat
diaphragm muscle (DIAm), 2 wks of unilateral denervation (DNV) or
tetrodotoxin (TTX) 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 ATPase
activities of type I, IIx and IIb fibers in DNV and TTX DIAm 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 DIAm.
These results suggest that disruption of neurotrophic influence has a
greater impact on muscle fiber metabolic properties than inactivity
per se.
Received 27 June 1996; accepted in final form 20 November 1996.
APS Manuscript Number A609-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996