Myosin heavy-chain composition in striated muscle after tenotomy.

The myosin heavy-chain (MHC) isoform pattern was studied by biochemical methods in the slow-twitch (soleus) and fast-twitch (gastrocnemius) muscles of adult rats during atrophy after tenotomy and recovery after tendon regeneration. The tenotomized slow muscle atrophied more than the tenotomized fast muscle. During the 12 days after tenotomy the total MHC content decreased by about 85% in the slow muscle, and only by about 35% in the fast muscle. In the slow muscle the ratio of MHC-1 to MHC-2A(2S) remained almost unchanged, showing that similar diminution of both isoforms occurs. In the fast muscle the MHC-2A/MHC-2B ratio decreased, showing the loss of MHC-2A mainly. After tendon regeneration, the slow muscle recovered earlier than the fast muscle. Full recovery of the muscles was not observed until up to 4 months later. The embryonic MHC, which seems to be expressed in denervated adult muscle fibres, was not detected by immunoblotting in the tenotomized muscles during either atrophy or recovery after tendon regeneration. The influence of tenotomy and denervation on expression of the MHC isoforms is compared. The results show that: (a) MHC-1 and MHC-2A(2S) are very sensitive to tenotomy, whereas MHC-2B is much less sensitive; (b) expression of the embryonic MHC in adult muscle seems to be inhibited by the intact neuromuscular junction

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

Eur J Biochem. 1990 Nov 13;193(3):623-8. Myosin heavy chain isoform composition in striated muscle after denervation and self-reinnervation. Jakubiec-Puka A, Kordowska J, Catani C, Carraro U. Source Laboratory of Protein Metabolism, Nencki Institute of Experimental Biology, Warsaw, Poland. Abstract 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 found in the MHC isoforms. Within 2 months of recovery a tendency to normalization was observed. The results show that (a) MHC-2B isoform and the morphological characteristics of the 2B-type muscle fibres are susceptible to lack of innervation, similar to those of type 1, (b) during muscle recovery induced by reinnervation the MHC isoforms and muscle fibres shift transiently to type 1 in the soleus and to type 2A in the extensor digitorum longus muscles, and (c) the embryonic isoform of MHC may appear in the adult skeletal muscles if innervation is disturbed. PMID: 2249683 [PubMed - indexed for MEDLINE] Free full tex