Abstract
Twelve weeks old male Wistar rats were separated into the pre- and post-experimental control, functional overload (FO), hindlimb-unloading (U), deafferentation (DA) and FO+DA groups. The tendons of the synergists of soleus muscle were transected in the FO rats. The continuous tail suspension was performed in the U rats. The dorsal roots of the L4-5 segmental levels of the spinal cord were transected in the DA rats. The sampling of the soleus muscle was performed before and 14 days after each treatments. Hypertrophy (+24%) of muscle fibers, associated with increased number of nucleoli within a single myonucleus, was induced by FO. The FO also increased the expression of the phosphorylated ribosomal protein S6 (S6) (+84%). Although the fiber size (-52%) and the expression of the phosphorylated S6 (-98%) was remarkably decreased following U, the nucleolar number was unchanged. Responses to DA were basically similar to those to U, although the magnitude of the effect was minor. The DA-related responses of these parameters were prevented by further addition of FO. FO+DA also resulted in the increase of the nucleolar number. These results suggested that the intranuclear number of nucleoli, which is stimulated by FO, may play an important role in the rate of protein synthesis and fiber size. [J Physiol Sci. 2007;57 Suppl:S95]
