Plasticity of skeletal myosin in endurance-trained rats (I). A quantitative study

The aim of this study was to quantify modifications in the expression of skeletal myosin light chain (MLC) and myosin heavy chain (MHC) isoforms of five muscles, according to their fiber composition and function, following endurance training in rats. Rodents were assigned randomly to one of two groups: caged sedentary controls (C) or endurance-trained rats (T). In T rats, three out of the four fast and mixed muscles studied exhibited a significant increase in the expression of MLC1s, 1f and 2s and a significant decrease in MLC2f and 3f, the exception being the plantaris muscle. In two out of the four muscles we observed a significant increase in MHCI and IIa, the exception being both gastrocnemii, where the expression of MHCI did not change. In the soleus of T rats, the expression of MLC1s, 2f and 3f decreased significantly, while that of MLC2s increased significantly, compared with those of C rats. The expression of MHCIIa in T rats decreased significantly compared with that of C rats, while the expression of MHCI increased significantly. In all muscles studied, a significant slowing of myosin isoforms was observed after endurance training.