AJP - Regulatory, Integrative and Comparative Physiology, Vol 270, Issue 1 80-R85, Copyright © 1996 by American Physiological Society
Regulation of succinate dehydrogenase within muscle fiber compartments by nerve-mediated activity and CNTF
R. N. Michel, R. J. Campbell and B. J. Jasmin
Department of Chemistry and Biochemistry, Laurentian University, Sudbury, Ontario, Canada.
We investigated the regulatory effects of neural activation and trophic
factors on the selective accumulation of succinate dehydrogenase (SDH; EC
1.3.99.1) activity at the endplate, as well as within subsarcolemmal and
intermyofibrillar regions of rat soleus muscle fibers. The role of
activation was assessed by stimulation of tetrodotoxin (TTX)-inactivated
nerves distal to the site of drug application. We also studied whether
ciliary neurotrophic factor (CNTF) is involved in regulating the
postsynaptic accumulation of SDH. Using quantitative microphotometry, we
found that daily stimulation of quiescent but intact nerves prevented the
TTX-induced decrease in SDH activity within extrajunctional regions,
whereas, at the endplate, the counteraction was partial (30%). Thus it
appears that endplate levels of this enzyme are regulated by a complex
mechanism involving an interaction between neuromuscular activation and
trophic factors. We also found that daily CNTF administration counteracted
the denervation-associated loss of SDH activity exclusively within the
intermyofibrillar compartment, suggesting that CNTF treatment mimics the
effects of activity on SDH levels within the core region of denervated
fibers, but under these conditions does not influence the endplate
accumulation of this enzyme.
