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

Background & Aims: Nitric oxide, a putative cellular messenger synthes ized from L-arginine, is a powerful modulator of gastric motility and secretions. The aim of this study was to investigate whether (1) guine a pig gastric chief cells express NO synthase, (2) NO modulates the pe psinogen secretion and guanosine 3',5'-cyclic monophosphate (cGMP) gen eration induced by calcium (Ca2+)-mediated agents, and (3) NO donors a nd cGMP analogues stimulate pepsinogen release. Methods: Chief cells w ere prepared by sequential digestion with collagenase and Ca2+ chelati on. NO generation was measured by determining the NO coproduct citrull ine. Results: NO synthase immunoreactivities were constitutively expre ssed in approximately 70% chief cells. Carbachol (10 mu mol/L) caused a 4-6-fold increase in pepsinogen release, citrulline generation, intr acellular 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 sy nthase activity. [Ca2+](i) chelator and calmodulin antagonist inhibite d the carbachol-induced pepsinogen secretion and NO generation. Preinc ubating the cells with L-NMMA had no effect on carbachol-stimulated in ositol triphosphate generation or [Ca2+](i) or Ca2+-dependent adenosin e triphosphatase levels. Nitrovasodilator agents and 8-bromo-cGMP stim ulated pepsinogen release. Conclusions: Gastric chief cells express a Ca2+/calmodulin-dependent NO synthase. NO modulates the stimulatory ef fect of Ca2+-mediated agonists on pepsinogen release.