Myosin and SERCA isoform expression in denervated slow-twitch muscle of euthyroid and hyperthyroid rabbits.

Changes in the isoform patterns of myosin heavy chains (MHC) and Ca2+-ATPase (SERCA) were studied in long-term (72 days) denervated slow-twitch soleus muscles of euthyroid and hyperthyroid rabbits. MHC isoforms were separated electrophoretically. SERCA isoforms were assessed by electrophoretic separation of the trypsin-digested and phosphorylated fragments. Denervation led to pronounced slow-to-fast transitions with increases in the fast MHC and fast SERCA1a isoforms. Hyperthyroidism had no significant effect on the denervation-induced changes in SERCA isoforms, but led to slight increases in the relative concentrations of the fast MHC isoforms. A high correlation existed between the relative concentrations of slow myosin and SERCA2a in both innervated euthyroid and hyperthyroid soleus muscles. This correlation, however, seems to be less tight in denervated soleus muscles.