Myosin heavy chain composition in regenerating skeletal muscle grafts

To study myosin heavy chain (MHC) composition during regeneration, nerve reimplanted autografting of extensor digitorum longus muscle (EDL) was performed in young Wistar rats. 5-8% gradient sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) was performed to separate MHC isoforms. Quantitative changes in MHC isoforms were determined densitometrically at the 10th, 30th and 60th day after autografting in grafted and non, grafted muscles. Ten days after grafting in control muscles MHCIIb represented similar to 64% and MHCIId/IIa similar to 36% from total MHC in the nongrafted EDL. In the grafted muscles MHCIIb decreased to similar to 27% and MHCIId\IIa increased to similar to 73% from total MHC presented. Thirty days after grafting MHCIIb corresponded similar to 57% and MHCIId\IIa similar to 43% from total MHC in the nongrafted EDL muscles. In the grafted muscles, MHCIIb decreased and represented similar to 2% while MHCIId\IIa represented similar to 98% from total MHC. Sixty days after grafting MHCIIb represented similar to 42% and MHCIId\IIa similar to 58% from total MHC in the nongrafted EDL muscles, but in the grafted muscles MHCIIb was not detected and thus, the regenerated EDL muscles contained only MHCIId\IIa isoforms. These data indicate, that MHC composition shifts from heterogeneous composition to homogenous slower type of MHC, which is regulated by the cycle of denervation and reinnervation in regenerating skeletal muscle fibers.