Role(s) of Mechanical Load and Satellite Cells in The Regulation of The Size of Soleus Muscle Fiber in Rats

Abstract

Roles of mechanical load and satellite cells in the regulation of morphological properties of soleus muscle fibers were reviewed. Gravitational unloading by exposure to microgravity and/or by hindlimb suspension causes passive plantarflexion of ankle joints, which then shortens the length of muscle fibers and sarcomeres. Such phenomena cause the decrease of tension development. Atrophy of muscle fibers caused by inhibited protein synthesis is induced in association with decreased number and increased size of myonuclei. Distribution of satellite cells, which serve as a source of new myonuclei during regeneration after a muscle injury and/or atrophy, also decreases in response to lowered mechanical load. However, these responses are generally reversible, when the mechanical load applied to muscle fibers is increased, suggesting that satellite cells play important role(s) in the regulation of muscle fiber properties. The data also indicated that one of the satellite cell-related regulations of muscle fiber was mechanical load-dependent, which was influenced by the sarcomere length.