[Sarcomeric cytoskeletal proteins and myosin phenotype in stretched soleus of hindlimb-suspended rats].

Changes in sarcomeric cytoskeletal proteins of rat m. soleus fibers upon the chronic stretching against the background of gravitational unloading were analyzed and compared with changes in fiber size and myosin phenotype. For rats exposed to gravitational unloading in the usual microgravity-simulating experimental model (hindlimb suspension (HS) according to Morey-Holten), a considerable reduction in the mass of m. soleus (by 54%) and the area of its fibers of both slow-twitch (by 47%) and fast-twitch (37%) types compared with control animals was revealed. Moreover, the percent of fibers containing only slow isoforms of myosin heavy chains (MHC) for suspended animals was slightly smaller and the portion of fibers interacting only with antibodies against fast myosin isoforms was significantly higher than for control animals. For hindlimb-suspended rats, the titin/MHC and nebulin/MHC ratios appeared to be reduced almost by two times as compared with those for the contriol group of animals. Chronic immobilization of m. soleus in stretched state against the background of suspension leads to a partial or complete prevention of the reduction in muscle fiber sizes, the transformation of the myosin phenotype into fast one, and a decrease in relative content of sarcomeric cytoskeletal proteins.