The Role of Antioxidant Enzymes in the Control of Opossum Gallbladder Motility

Abstract

Background. Superoxide rapidly oxidizes nitric oxide (NO) to form peroxynitrite, thus terminating the biological activity of NO. The aims of our study were to determine if superoxide alters the motor function of the gallbladder and to localize the antioxidant enzymes in the gallbladder.Materials and methods. Immunostaining and immunoblots were performed and enzyme activities were measured in the gallbladder. In physiologic experiments, force-displacement transducers recorded tension in gallbladder muscle strips. Superoxide was generated by the addition of xanthine with xanthine oxidase, while superoxide radicals were scavenged by the addition of superoxide dismutase (SOD) and catalase. SOD was inhibited by deithyldithiocarbamate.Results. Immunostaining demonstrated superoxide dismutase and catalase immunoreactivity in ganglia situated throughout the smooth muscle. Total superoxide dismutase activity was 115 ± 12 U/mg. Western blots detected expression of proteins of 19.4 kDa for copper/zinc SOD and 25.0 kDa for manganese SOD. Generation of superoxide increased isometric tension, while pretreatment with SOD prevented the increase in isometric tension induced by superoxide. Inhibition of SOD diminished the EFS-induced off response.Conclusions. We conclude that superoxide alters gallbladder motor function, and the presence of superoxide scavenging enzymes in enteric plexuses suggests that they may regulate gallbladder neuromuscular function by clearing endogenous superoxide.