Biochemical studies of the external anal sphincter muscle of the rabbit

Abstract

The biochemical characteristics of the external anal sphincter muscle of rabbits were compared with those of extensor digitorum longus and soleus muscles of rabbits. The light chains of the myosin of external anal sphincter were found to be composed of three chains, and their electrophoretic mobilities were the same as those of extensor digitorum longus. The myosin adenosine triphosphatase (ATPase) activity was low in comparison to that of extensor digitorum longus, but actomyosin ATPase activity was the same. The pH-activity profile of the myosin ATPase of external anal sphincter was qualitatively similar to that of extensor digitorum longus. The effects of KCl and GEDTA on the actomyosin ATPase activity of external anal sphincter were less pronounced than those of extensor digitorum longus muscle and were similar to those of soleus muscle. The electrophoretic mobilities of the three subunits of the troponin of external anal sphincter were the same as those of the respective subunits of extensor digitorum longus muscle, but the mobility of the troponin-I component of external anal sphincter is definitely different from that of soleus. The isozyme pattern of the lactic dehydrogenase of external anal sphincter closely approximated that of extensor digitorum longus. These results suggest that, from the biochemical point of view, external anal sphincter is similar to extensor digitorum longus muscle or fast-twitch fibers in spite of physiologic properties of the sphincter muscle which are suggestive of slow-twitch fibers.