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 sk eletal myosin light chain (MLC) and myosin heavy chain (MHC) isoforms of fi ve muscles, according to their fiber composition and function, following en durance training in rats. Rodents were assigned randomly to one of two grou ps: caged sedentary controls (C) or endurance-trained rats (T). In T rats, three out of the four fast and mixed muscles studied exhibited a significan t increase in the expression of MLCls, If and 2s and a significant decrease in MLC2f and 3f, the exception being the plantaris muscle. In two out of t he four muscles we observed a significant increase in MHCI and IIa, the exc eption being both gastrocnemii, where the expression of MHCI did not change . In the soleus of T rats, the expression of MLC2f and 3f decreased signifi cantly, while that of MLC2s increased significantly, compared with those of C rats. The expression of MHCIIa in T rats decreased significantly compare d with that of C rats, while the expression of MHCI increased significantly . In all muscles studied, a significant slowing of myosin isoforms was obse rved after endurance training.