Role of PGE2 on gallbladder muscle cytoprotection of guinea pigs.

H2O2 and taurochenodeoxycholic acid (TCDC) impair the contraction induced by CCK-8, ACh, and KCl without affecting the actions of PGE2 and damage functions of membrane proteins except for PGE2 receptors. The aim of this study was to examine whether the preserved PGE2 actions contribute to cytoprotective mechanisms against reactive oxygen species. Muscle cells from guinea pig gallbladder were obtained by enzymatic digestion. Levels of lipid peroxidation and activities of SOD and catalase were determined by spectrophotometry. Pretreatment with PGE2 prevented the inhibition of H2O2 or TCDC on agonist (CCK-8, ACh, and KCl)-induced contraction and reduced the expected increase in lipid peroxidation and activities of catalase and SOD caused by H2O2 and TCDC. Incubation with CCK-8 for 60 min desensitized CCK-1 receptors up to 30 min, whereas no receptor desensitization was observed after PGE2 pretreatment. Cholesterol-rich liposome treatment enhanced the inhibition of H2O2 and TCDC on agonists-induced contraction, including that of PGE2. Pretreatment with PGE2 before H2O2 and TCDC did not completely block their inhibition on agonist-induced contraction. Cholesterol-rich liposome treatment impaired the expected increase in catalase activities in response to PGE2. We conclude that pretreatment with PGE2 prevents the muscle cell damage caused by H2O2 and TCDC due to the resistance of PGE2 receptors to agonist-induced desensitization. The preservation of PGE2 receptors may be designed to conserve these cytoprotective functions that are, however, impaired by the presence of excess cholesterol in the plasma membrane.