Roles of Ca2+ and protein kinase C in regulation of prostaglandin E2 release by cultured rabbit gastric epithelial cells

Prostaglandin (PG) has been reported to be one of the important protective factors in the gastric mucosa. However the mechanism of the regulation of endogenous PG production has not been well studied. We investigated the possible roles of Ca²⁺, cAMP, and protein kinase C (PKC) in the regulation of PGE₂ release from cultured rabbit gastric mucosal cells. PGE₂ was measured by radioimmunoassay. A23187 (Ca²⁺ ionophore) at 2×10^?6 M significantly increased PGE₂ release. Deprivation of Ca²⁺ from the medium blocked the A23187-induced increase of PGE₂. TMB-8 (a putative inhibitor of Ca²⁺ release from intracellular stores) did not have any significant effects on the increase of PGE₂-induced by A23187. Thus, A23187 increased PGE₂ through the influx of extracellular Ca²⁺. W7 or compound 48/80 (calmodulin inhibitors) did not alter the response of PGE₂ caused by A23187. Exogenous administration of cAMP, forskolin (an activator of adenylate cyclase), or 2-chloroadenosine (a possible activator of adenylate cyclase through adenosine A₂ receptor) had neither significant effects on PGE₂ release nor an effect on A23187-induced increase of PGE₂ release. 12-O-tetradecanoylphorbol 13-acetate (TPA, an activator of PKC) significantly stimulated PGE₂ release in a dose-dependent fashion, whereas another phorbol ester with no biological activity did not. A23187 at 0.8×10^?6 M, but not cAMP, potentiated the TPA-induced increase of PGE₂. Mepacrine (a phospholipase A₂ inhibitor) reduced the A23187-and TPA-induced increase of PGE₂. These results suggest that Ca²⁺ and protein kinase C may play important roles in the regulation of PGE₂ release by cultured rabbit gastric cells.