NITRIC-OXIDE MODULATES PEPSINOGEN SECRETION INDUCED BY CALCIUM-MEDIATED AGONIST IN GUINEA-PIG GASTRIC CHIEF CELLS

Background & Aims: Nitric oxide, a putative cellular messenger synthesized from L-arginine, is a powerful modulator of gastric motility and secretions. The aim of this study was to investigate whether (1) guinea pig gastric chief cells express NO synthase, (2) NO modulates the pepsinogen secretion and guanosine 3',5'-cyclic monophosphate (cGMP) generation induced by calcium (Ca2+)-mediated agents, and (3) NO donors and cGMP analogues stimulate pepsinogen release. Methods: Chief cells were prepared by sequential digestion with collagenase and Ca2+ chelation. NO generation was measured by determining the NO coproduct citrulline. Results: NO synthase immunoreactivities were constitutively expressed in approximately 70% chief cells. Carbachol (10 mu mol/L) caused a 4-6-fold increase in pepsinogen release, citrulline generation, intracellular Ca2+ concentration ([Ca2+](i)) and cGMP concentration. These effects were concentration dependently inhibited by N-G-monomethyl-L-arginine (L-NMMA). As gastrin, cholecystokinin, thapsigargin, and Ca2+ ionophore increased NO generation, [Ca2+](i) seemed to regulate NO synthase activity. [Ca2+](i) chelator and calmodulin antagonist inhibited the carbachol-induced pepsinogen secretion and NO generation. Preincubating the cells with L-NMMA had no effect on carbachol-stimulated inositol triphosphate generation or [Ca2+](i) or Ca2+-dependent adenosine triphosphatase levels. Nitrovasodilator agents and 8-bromo-cGMP stimulated pepsinogen release. Conclusions: Gastric chief cells express a Ca2+/calmodulin-dependent NO synthase. NO modulates the stimulatory effect of Ca2+-mediated agonists on pepsinogen release.