The role of antioxidant enzymes in the control of opossum gallbladder motility

Background. Superoxide rapidly oxidizes nitric oxide (NO) to form peroxynit rite, thus terminating the biological activity of NO. The aims of our study were to determine if superoxide alters the motor function of the gallbladd er and to localize the antioxidant enzymes in the gallbladder. Materials and methods. Immunostaining and immunoblots were performed and en zyme activities were measured in the gallbladder. In physiologic experiment s, force-displacement transducers recorded tension in gallbladder muscle st rips. Superoxide was generated by the addition of xanthine with xanthine ox idase, while superoxide radicals were scavenged by the addition of superoxi de dismutase (SOD) and catalase. SOD was inhibited by diethyldithiocarbamat e. Results. Immunostaining demonstrated superoxide dismutase and catalase immu noreactivity in ganglia situated throughout the smooth muscle. Total supero xide dismutase activity was 115 +/- 12 U/mg. Western blots detected express ion of proteins of 19.4 kDa for copper/zinc SOD and 25.0 kDa for manganese SOD. Generation of superoxide increased isometric tension, while pretreatme nt with SOD prevented the increase in isometric tension induced by superoxi de. 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 sugg ests that they may regulate gallbladder neuromuscular function by clearing endogenous superoxide. (C) 1999 Academic Press.