A Low Temperature Environment Delays the Changes in Muscle Fiber Type Composition Induced by Unloading

抄録

The present study examined whether low-temperature (LT) could reduce experimentally-induced atrophy of the skeletal muscle in non-hibernating mammals, as judged by muscle wet-weight, cross-sectional area of muscle fibers, ratio of muscle fiber types, and number of apoptotic myofibers in the soleus muscle of rat. Hindlimb unloading (HU) was carried out for either one or two weeks (1W or 2W, respectively) at room temperature (HU-1W and HU-2W groups) or LT (10°C, HULT-1W and HULT-2W groups). Other animals were allowed to move freely at either room temperature (CON-1W and CON-2W groups) or LT (LT-1W and LT-2W groups). Total caloric intake was increased in LT rats compared with the CON, HULT and HU rats. Body weight, muscle wet-weight and cross-sectional area were significantly decreased in HU and HULT rats compared with CON and/or LT rats. Type-I fiber composition in HULT-2W was not significantly reduced compared with those of CON-2W and LT-2W, but that of HU-2W was significantly reduced compared with the other groups. A small number of caspase-3-activated myofibers appeared in HULT-2W and HU-2W, but not in CON-2W and LT-2W. Thus, our results indicate that LT retards the change in the ratio of type-I and type-II fibers, but does not prevent decreases in muscle size and mass, or apoptosis of myofibers.