Signal transduction pathway in gastric mucous cells

In isolated and enriched guinea-pig gastric mucous cells the effects of carbachol, prostaglandin E2 (PG E2), prostaglandin F2 alpha (PG F2 alpha) and histamine on adenylate cyclase (AC) and cytosolic free Ca2+ were investigated, in order to study the biochemical mechanisms involved in secretagogue-mediated mucus release. Histamine and both prostaglandins stimulated AC in partially purified membranes of mucous cells. Histamine was most efficacious, followed by PG E2 and PG F2 alpha. The histamine effect was blocked by the H2-receptor antagonist ranitidine, but not by the H1-receptor antagonist mepyramine. Carbachol raised the resting [Ca2+]i in mucous cells from 120 to 306 nM. This carbachol effect was blocked by atropine. Histamine and PG E2 stimulation of AC was inhibited in a concentration-dependent manner by Ca2+ (IC50:31 microM). In the presence of TPA and phosphatidylserine, conditions which activate protein kinase C, the inhibitory action of Ca2+ on AC was significantly increased. These data indicate that there exists a negative feedback control mechanism between protein kinase C and histamine/prostaglandin E2-induced AC activation. From the finding that TPA and phosphatidylserine increased the inhibitory action of Ca2+ on cholera toxin-, but not on forskolin-stimulated AC we assume that the point, where protein kinase C exerts its inhibitory effect at the AC, is the guanine nucleotide regulatory protein.