Influence of overload on phenotypic remodeling in regenerated skeletal muscle

We studied the effects of 10 wk of functional overload on the expression of myosin heavy chain (MHC), sarcoplasmic reticulum Ca2+-ATPase isoforms (SER CA), and the activity of several metabolic enzymes in sham and regenerated plantaris muscles. Overload was accomplished by bilateral surgical ablation of its synergists 4 wk after right plantaris muscles regenerated after myo toxic infiltration. The overload-induced muscle enlargement was slightly le ss in regenerated than in sham muscles [28% (P< 0.005) and 43% (P< 0.001), respectively]. Overload led to an increase in type I MHC expression (P< 0.0 1) to a similar extent in sham and regenerated plantaris, while the expecte d shift from type IIb to type IIa MHC was less marked in regenerated than i n sham plantaris. The overload-induced decrease in the expression of the fa st SERCA isoform and in the activity of the M subunit of lactate dehydrogen ase occurred to a similar extent in sham and regenerated plantaris [66% (P< 0.01) and 27% (P< 0.005), respectively]. In conclusion, the lesser respons es of muscle mass and fast MHC composition of regenerated plantaris to mech anical overload suggest an alteration of the transcriptional, translational , and/or posttranslational control of gene expression in regenerated muscle .