SUCCINATE-DEHYDROGENASE ACTIVITY WITHIN SYNAPTIC AND EXTRASYNAPTIC COMPARTMENTS OF FUNCTIONAL-OVERLOADED RAT SKELETAL-MUSCLE FIBERS

Activity of the mitochondrial enzyme succinate dehydrogenase (SDH) was assessed using quantitative microphotometric techniques within postsy naptic, subsarcolemmal and intermyofibrillar compartments of overloade d soleus muscle fibers. Six weeks of overload, induced via synergist t enotomy, significantly increased soleus muscle mass (23%) and mean fib er cross-sectional area (17%). Despite these increases in cell size, S DH activity within all three intracellular compartments of overloaded muscle fibers was not different from levels in corresponding regions o f control fibers. Thus, we show for the first time that activity-relat ed increases in muscle cell volume, and specifically motor endplate ar ea, appear to be coordinated with increased levels of oxidative enzyme s within distinct subcellular compartments, including the postsynaptic sarcoplasm.