REGULATION OF MYOSIN HEAVY-CHAIN EXPRESSION IN ADULT-RAT HINDLIMB MUSCLES DURING SHORT-TERM PARALYSIS - COMPARISON OF DENERVATION AND TETRODOTOXIN-INDUCED NEURAL INACTIVATION

The extent to which myosin profiles within adult fast and slow muscles are altered by short-term paralysis remains equivocal. We used an arr ay of specific antibodies to identify adult and developmental MHC isof orms within EDL and soleus muscle fibers, and show a marked multiple e xpression of MHCs with a general shift towards slower and more energy efficient MHC profiles after 2 weeks of denervation or TTX nerve condu ction block, Paralysis also induced marked expression of an embryonic MHC within most EDL cell types, and a subtle, paralysis-sensitive, exp ression of alpha-cardiac MHC within specific EDL and soleus extrafusal fibers, Comparison of treatment groups also permitted assessment of t he relative influence of neural activity versus trophic factors on the se isoforms, and confirmed activity as a major, but not sole, regulato r of MHC expression.