Abstract
We investigated the changes in fiber type composition and myosin heavy chain isoform in rat soleus muscles during 7-week hindlimb suspension. In the soleus muscles, a significant reduction of the muscle weight was observed after 3-week suspension, and the muscle fiber atrophy was found in both slow-twitch oxidative (SO) and fast-twitch oxidative glycolytic (FOG) fibers. This indicates that the decrease in the muscle weight was caused by the atrophy of both SO and FOG fibers. As for the fiber type composition, the percentage of FOG fibers increased in the soleus muscles after 3-week suspension, and concomitantly an increase in the fast type of myosin heavy chain isoform was also observed. These results suggest that the increase in the percentage of FOG fibers in the soleus muscles during hindlimb suspension was caused by the conversion from SO to FOG fibers, it is also suggested that the increase in FOG fibers reflected that of fast type of myosin heavy chain isoform. The speeding of the soleus muscles following hindlimb suspension was considered from both tissue level by histochemical analysis and molecular level by SDS-PAGE and immunobiochemical analysis.
