Contractile protein concentrations in human single muscle fibers.

The intent of this investigation was twofold: (1) to develop a convenient method for analyzing skeletal muscle protein concentrations in a large number of individual human single fibers and (2) to compare the myosin heavy chain (MHC) and actin concentrations in fibers expressing pure MHC I or MHC IIa. Individual vastus lateralis fibers were dissected from five individuals (3 M, 2 F; 24 +/- 1 years) and used to determine single fiber total protein (TP) concentration and MHC distribution. Fibers expressing pure MHC I and MHC IIa were further analyzed for MHC (252 fibers; mean of 50/subject) and actin (160 fibers; mean of 32/subject) concentration relative to TP. Single fiber MHC concentration was 26 +/- 4% greater (P < 0.05) in MHC IIa (364 +/- 39 micrograms MHC/mg TP) vs. MHC I (266 +/- 29 micrograms MHC/mg TP) fibers. No differences (P > 0.05) were noted in single fiber actin concentration (MHC I: 171 +/- 17 micrograms actin/mg TP; MHC IIa: 165 +/- 17 micrograms actin/mg TP). These data indicate that within the TP fraction, skeletal muscle fibers contain differing amounts of MHC, and this appears to be fiber type specific. These data and methods have implications for the study of human muscle fiber type specific alterations in various protein concentrations in response to exercise, models of unloading, and aging.