抄録
It has been well known that in skeletal muscle clenbuterol (CB, a beta-2-adrenergic agonist) promotes muscle hypertrophy as well as a fiber-type transition, whereas rapamycin (RAPA, a inhibitor of the mammalian target of rapamycin, mTOR) induces atrophy. To our knowledge, the interaction between the two drugs at the cellular level has not been studied. To gain more insight into the molecular mechanism of muscle growth and fiber-type transformations, we analyzed the effects of CB and/or RAPA on the diameter of muscle fibers as well as on the fiber-type composition in rat soleus muscle by using a immunohisochemical method with anti-fast and slow-type myosin heavy chain antibodies. As compared with control, the diameter of fast, slow and mixed fibers were significantly increased by the CB treatment (p<0.05) but decreased by the RAPA treatment (p<0.05), while that of these fibers did not change with the CB+RAPA treatment. The CB, RAPA and CB+RAPA treatments significantly (p<0.05) increased the relative contents of fast and mixed fibers at the expense of that of slow fibers. These results suggest that in rat soleus muscle the CB treatment as well as the RAPA treatment induce the slow-to-fast fiber-type transition, while the CB treatment induces the muscle hypertrophy, which is antagonized by rapamycin. [J Physiol Sci. 2007;57 Suppl:S96]
