Responses of the morphological and metabolic properties of soleus muscle to reduced contractile activity and/or aging

Abstract

It is well known that skeletal muscle fibers atrophy in response to reduced contractile activity, gravitational unloading, and/or aging. However, the molecular mechanisms responsible for such muscular responses are still unclear. Muscle fiber atrophy induced by gravitational unloading generally is associated with the shift of fiber phenotype toward fast-twitch type. But the soleus muscle in aged rat is composed of more slow-fibers than young rat, although fiber atrophy is induced. Therefore, it is suggested that the fiber size and phenotype are regulated by different mechanisms. Possible mechanisms responsible for the regulation of morphological and/or metabolic properties of skeletal muscle in response to contractile activity or aging, as well as the countermeasures for prevention of muscle atrophy, will be discussed in the symposium. [Jpn J Physiol 54 Suppl:S31 (2004)]