EFFECT OF EBROTIDINE ON GASTRIC-MUCOSAL CALCIUM-CHANNEL ACTIVITY

Ebrotidine is a new H2-receptor antagonist also known for its gastropr otective effect against ethanol-induced mucosal injury. In this study, we investigated the effect of ebrotidine on the activity of the gastr ic mucosal calcium channels. The channel complex was isolated from the solubilized gastric epithelial cell membranes by affinity chromatogra phy on wheat germ agglutinin. After being labeled with [H-3]PN200-110, the complex was reconstituted into phosphatidylcholine vesicles which exhibited active Ca-45(2+) uptake into intravesicular space and respo nded in a concentration-dependent manner to calcium channel activator, BAY K8644, as well as to calcium channel antagonist, PN200-110. The C a-45(2+) uptake was inhibited by ebrotidine. Maximum inhibitory effect was attained at 50 mug/ml ebrotidine, at which point a 54.9% decrease in uptake occurred. The gastric mucosal calcium channels, on epiderma l growth factor binding (EGF) in the presence of ATP, responded by an increase in tyrosine phosphorylation of 55 and 170 kDa proteins, and t he vesicles containing the phosphorylated channels displayed a 48% gre ater Ca-45(2+) uptake. This phosphorylation process was inhibited by e brotidine. Furthermore, ebrotidine also interfered with the binding of EGF to calcium channel protein. The results point toward the importan ce of EGF in the maintenance of gastric mucosal calcium homeostasis, a nd suggest that ebrotidine has the ability to protect the cellular int egrity from calcium imbalance by modulating the EGF-stimulated gastric mucosal calcium channel phosphorylation.