Endurance training-induced changes in alkali light chain patterns in type IIB fibers of the rat.

The effects of endurance training on the expression of myosin were electrophoretically analyzed in the deep portion of vastus lateralis muscle from the rat. A 10-wk running program led to increases (P < 0.01) in myosin heavy chain (MHC) 2a and 2d with a decrease (P < 0.01) in MHC(2b). Training also evoked a rearrangement of the isomyosin pattern with decreases in fast isomyosin (FM) 1 (P < 0.01) and FM2 (P < 0.05) and a rise in intermediate isomyosin (P < 0.01). These changes were accompanied by a 61% decrease (P < 0.01) in myosin light chain (MLC) 3F (11.8 +/- 2.7 vs. 4.6 +/- 4.2%). Two-dimensional electrophoresis made it possible to separate the triplet of isomyosins (FMb) consisting of MHC(2b). Training elicited a 26% decrease (P < 0.05) in the FM1b fraction within FMb, i.e., FM1b/(FM1b + FM2b + FM3b) (24.2 +/- 5.5 vs. 18.0 +/- 4.3%). These changes resulted in a 10% decrease (P < 0.05) in the MLC(3F) fraction, i.e., MLC(3F)/(MLC(1F) + MLC(3F)), in FMb (44.9 +/- 4.5 vs. 40.3 +/- 3.2%). These results suggest that endurance training may exert the depressive effect on the contractile velocity of type IIB fibers and that a training-induced decrease in the contractile velocity of whole muscle may be caused by alterations in fast alkali MLC complements within a given fiber type as well as by transitions in MHC-based fiber populations.