Effects of aging on actin sliding speed on myosin from single skeletal muscle cells of mice, rats, and humans

The effects of aging on the mechanical properties of myosin were measured i n 87 fibers from muscles of humans (n = 40), rats (n = 21), and mice (n = 2 6) using a single fiber in vitro motility assay. Irrespective of species, a n 18-25% aging-related slowing in the speed of actin filaments was observed from 62 single fibers expressing the slow (type I) beta -myosin heavy chai n isoform. The mechanisms underlying the aging-related slowing of motility speed remain unknown, but it is suggested that posttranslational modificati ons of myosin by oxidative stress, glycation, or nitration play an importan t role. The aging-related slowing in the speed of actin filaments propelled by the type I myosin was confirmed in three mammalian species with an simi lar to3,400-fold difference in body size. Motility speed from human myosin was 3-fold slower than from myosin of the similar to3,400-fold smaller mous e and approximately twofold slower when compared with the similar to 130-fo ld smaller rat, irrespective of age. A strong correlation was observed betw een the log values of actin sliding speed and body mass, suggesting that th e effects of scaling is, at least in part, due to altered functional proper ties of the motor protein itself.