Abstract
Carbonic anhydrase III (CAIII) is expressed selectively in type I (slow‑twitch) myofibers. To investigate the association between changes in the expression of CAIII and skeletal muscle structure following denervation, the present study stained adjacent sections of skeletal muscle for ATPase and immunohistochemically for CAIII. In addition, differences in the protein expression and phosphatase activity of CAIII were examined by western blot and phosphatase staining between rat soleus and extensol digitorum longus (EDL) muscles, which are composed of predominantly slow‑ and fast‑twitch fibers, respectively. Upon denervation, the EDL muscle showed more pronounced structural changes, compared with the soleus muscle. There was a transformation from fast to slow fibers, and a concomitant increase in fibers positive for CAIII. Following denervation, the protein expression of CAIII initially increased and then decreased in the soleus muscle, whereas the protein expression of CAIII in the EDL muscle increased gradually with time. In contrast to the protein changes, phosphatase activity in the soleus and EDL muscles decreased significantly following denervation. These results indicated that, following denervation, changes in the expression of CAIII were associated with myofiber remodeling. Specifically, the change in the expression of CAIII reflected the conversion to type I myofibers, suggesting the importance of CAIII in resistance to fatigue in skeletal muscle.