GASTRIN AND CCK ACTIVATE PHOSPHOLIPASE-C AND STIMULATE PEPSINOGEN RELEASE BY INTERACTING WITH 2 DISTINCT RECEPTORS

Both gastrin and cholecystokinin (CCK) can stimulate pepsinogen release from chief cells, but controversy exists about the receptors or intracellular mediators involved. In the present study, we prepared isolated chief cells from guinea pig stomach (>90% pure) to investigate the ability of gastrin and CCK to alter cell function. The COOH-terminal octapeptide of CCK (CCK-8) caused an eightfold increase in pepsinogen release (EC50), 54 nM). Both CCK-8 and gastrin increased inositol phosphates, with CCK-8 (1 muM) and gastrin (3 muM) causing a 40- and 14-fold increase in [H-3]IP1, 10- and 6-fold for [H-3]IP2, and 8- and 4-fold for [H-3]IP3. CCK-8 caused a half-maximal increase in [H-3]IP3 at 2 nM, and the dose-response curve was monophasic, whereas with gastrin the curve was biphasic, with an EC50 of the initial component (20% maximal) at 38 nM and the second component at 10 muM. L-364,718 (0.1 muM) inhibited the secondary increase seen with gastrin concentrations > 10 nM. The CCK-A-selective agonist A-71378 was 8590% as efficacious as CCK-8 and was equally potent. With 0.1 muM L-364,718, A-71378 caused no increase in [H-3]inositol phosphates until >10 nM, whereas CCK-8 caused 15% of maximal increase at concentrations >0.3 nM. Similar results were obtained with cytosolic calcium measured using fura-2 or on CCK-8- or gastrin-stimulated pepsinogen release. These results demonstrate that gastrin and CCK-8 can alter chief cell function by interacting with either a CCK-A or CCK-B/gastrin receptor. Both receptors are coupled to phospholipase C and cause changes in inositol phosphates, cytosolic calcium, and pepsinogen release; however, the intracellular amplification differs between the two receptor subtypes. Activation by CCK-related peptides of the CCK-A receptor subtype accounts for 85-90% of the maximal changes in cellular function, and activation of the CCK-B/gastrin receptor accounts for 10-20% of maximal changes.