Myosin heavy chain isoform composition in striated muscle after denervation and self-reinnervation

The total content of myosin heavy chains (MHC) and their isoform pattern were studied by biochemical methods in the slow‐twitch (soleus) and fast‐twitch (extensor digitorum longus) muscles of adult rat during atrophy after denervation and recovery after self‐reinnervation. The pattern of fibre types, in terms of ultrastructure, was studied in parallel. After denervation, total MHC content decreased sooner in the slow‐twitch muscle than in the fast‐twitch. The ratio of MHC‐1 and the MHC‐2B isoforms to the MHC‐2A isoform decreased in the slow and the fast denervated muscles, respectively. After reinnervation of the slow muscle, the normal pattern of MHC recovered within 10 days and the type 1 isoform increased above the normal. In the reinnervated fast muscle, the 2B/2A isoform ratio continued to decrease. Traces of the embryonic MHC isoform, identified by immunochemistry, were found in both denervated and reinnervated slow and fast muscles. A shift in fibre types was similar to that fou...