CHANGES OF THE EXPRESSION FOR THE STRESS PROTEINS IN RAT SKELETAL MUSCLES

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We performed two experiments in 2000-2002. One is the expression of heat shock proteins (HSPs) in regenerating rat soleus muscle, and the other is the expression of HSPs in hypertrophied rat soleus muscle.(1) The expression of HSPs in regenerating rat soleus muscle : the soleus muscle fibers were degenerated by injection of bupivacain. The regenerate fibers were observed at day 4 after the injection, and the fiber area gradually increased during recovery week 4. The HSP72 levels in regenerating fibers increased consistently with the growth for the regenerating fibers. These results may suggest that the HSP72 is related to the growth for the regenerating fibers.(2) The expression of HSPs in hypertrophied rat soleus muscle : soleus muscle fibers, especially the fast-twitch fibers, were hypertrophied by clenbuterol administration in drinking water for 4 weeks. The fiber type composition and the profiles of myosin heavy chain composition were changed toward "Fast" types in the slow soleus muscle treated with clenbuterol. Coexpression of myosin heavy chain isoforms were observed in the clenbuterol-treated soleus single fibers. However, the expression level of HSP72 was dramatically decreased in hypertrophied solesu muscle. Our results clearly indicate that the HSP72 was decreased in hypertrophied soleus muscle induced by clenbuterol, and suggest that the HSP72 is not related directly to the muscle hypertrophy.