MYOSIN HEAVY-CHAIN COMPOSITION OF REGENERATED SOLEUS MUSCLES DURING HINDLIMB SUSPENSION

The aim of this study was to determine the MHC profile of regenerated soleus muscles in control (C, n = 8) and hindlimb suspended rats (HS, n = 8). After muscle degeneration was induced by injection of snake ve nom containing notexin, male rats were either tail suspended for 21 da ys or submitted to normal weight-bearing activity. Separation and dete ction of MHCs by sodium dodecyl sulphate-polyarcylamide gel electropho resis (SDS-PAGE) showed that regenerated soleus muscles from C rats co ntained only type I and type Ila MHCs. The relative amount of type I M HC was higher in regenerated (93.9 +/- 1.7%) than in untreated muscles (86.5 +/- 2.3%) (P < 0.01). in the HS group, the immunohistochemical analysis showed that the majority of regenerated myofibres reacted pos itively with the antibody against fast MHCs. SDS-PAGE analysis demonst rated that HS resulted in a shift toward faster MHCs in both intact an d regenerated myofibres. Regenerated soleus muscle from HS rats contai ned approximate to 34% type Ila MHC, approximate to 37% type IIx/d MHC and approximate to 18% type IIb MHC, when type I MHC contributed to o nly approximate to 12% of total myosin. The proportions of fast MHC is oforms in regenerated muscles were higher than those recorded in untre ated muscles. Collectively, these results suggest that the shift in th e MHC profile associated with hindlimb unweighting in adult undamaged soleus muscles is also related to the heterogeneity of early myoblasts .