LACK OF TYPE-1 AND TYPE 2A MYOSIN HEAVY-CHAIN ISOFORMS IN RAT SLOW MUSCLE REGENERATING DURING CHRONIC NERVE BLOCK

The degeneration-regeneration process was induced by bupivacaine injec tion in innervated, denervated, and nerve-blocked rat soleus muscles. Nerve block was obtained by superfusion of the sciatic nerve with tetr odotoxin (mt), Two weeks after bupivacaine injection, immunohistochemi cal and electrophoretical analyses showed the presence of type 1 myosi n heavy chain (MHC) only in innervated regenerated muscles, type 2A in innervated and denervated, but not in mt-paralyzed muscles, and type 2X under all experimental conditions. The presence of type 1 MHC in th e innervated, and its absence in both denervated and TTX-paralyzed mus cles were also verified immunohistochemically I week after bupivacaine injection. It is concluded that the nerve impulses play a determinant role in the expression of 1 and 2A MHC isoforms in the innervated reg enerating muscle. The possible causes of the absence of the type 2A MH C isoform in the TTX-paralyzed muscles are discussed. (C) 1998 John Wi ley & Sons, Inc.