REGULATION OF SUCCINATE-DEHYDROGENASE WITHIN MUSCLE-FIBER COMPARTMENTS BY NERVE-MEDIATED ACTIVITY AND CNTF

We investigated the regulatory effects of neural activation and trophi c factors on the selective accumulation of succinate dehydrogenase (SD H; EC 1.3.99.1) activity at the endplate, as well as within subsarcole mmal and intermyofibrillar regions of rat soleus muscle fibers. The ro le of activation was assessed by stimulation of tetrodotoxin (TTX)-ina ctivated nerves distal to the site of drug application. We also studie d whether ciliary neurotrophic factor (CNTF) is involved in regulating the postsynaptic accumulation of SDH. Using quantitative microphotome try, we found that daily stimulation of quiescent but intact nerves pr evented the TTX-induced decrease in SDH activity within extrajunctiona l 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 administ ration counteracted the denervation-associated loss of SDH activity ex clusively within the intermyofibrillar compartment, suggesting that CN TF treatment mimics the effects of activity on SDH levels within the c ore region of denervated fibers, but under these conditions does not i nfluence the endplate accumulation of this enzyme.