Rat gastric mucosal adenylyl cyclase

Abstract

Prostaglandin E1, epinephrine, secretin, and glucagon are known inhibitors of gastric acid secretion, and each agent stimulated mucosal membrane (600 X g pellet) adenylyl cyclase activity from the corpus of the rat stomach. This adenylyl cyclase activity was also stimulated by 5'-guanylyl-imidodiphosphate and sodium fluoride but not by guanosine-5'-triphosphate. By contrast, the gastric acid secretagogues, pentagastrin, histamine, and carbachol, had no effect on basal or prostaglandin E1-stimulated mucosal adenylyl cyclase activity. Most of the sodium fluoride- and hormone-stimulated adenylyl cyclase of the corpus mucosa was contained in the 600 X g membrane fraction. The enzyme exhibited Michaelis-Menten kinetics with respect to the concentration of ATP, with an apparent Km of 0.25 mM. Histamine did not stimulate rat mucosal adenylyl cyclase activity under a variety of conditions, but did stimulate the same enzyme in guinea pig gastric fundic mucosa, an enzyme also activated by prostaglandin E1. These studies do not support the hypothesis that cyclic AMP mediates the actions of gastric acid secretagogues on the parietal cell in the rat.