Release of intracellular Ca 2+ and elevation of inositol trisphosphate by secretagogues in parietal and chief cells isolated from rabbit gastric mucosa

Abstract

The fluorescent intracellular Ca 2+ indicator, fura2/AM, was used to determine the effects of carbachol, cholecystokinin octapeptide (CCK-8), gastrin and histamine on intracellular Ca 2+ ([Ca 2+] i) in parietal cells from rabbit gastric mucosa enriched to more than 95% purity by a new Nycodenz gradient/centrifugal elutriation technique. Changes in [Ca 2+] i in response to the same agonists were also measured in enriched chief cells. Carbachol, histamine, gastrin and CCK-8 increased parietal cell [Ca 2+] i with the response to carbachol > CCK-8 = histamine = gastrin. Prestimulation with maximal doses of carbachol blocked histamine-induced increases in [Ca 2+] i. In chief cells, carbachol increased [Ca 2+] i but to a lesser degree than CCK-8, while histamine had no significant effect on [Ca 2+] i. Neither removal of extracellular Ca 2+ coupled with acute addition of 1 mM EGTA nor addition of the Ca 2+-channel blocker nicardipine prevented agonist-induced changes in [Ca 2+] i in either cell type. In the presence and absence of 10 mM LiCl 2, carbachol and CCK-8 were found to increase inositol trisphosphate (IP 3) content in both parietal and chief cells while histamine had no significant effect on this phosphoinositide hydrolysis product. From these results and previous observations with gastric glands (Chew, C.S. (1986) Am. J. Physiol. 13, G814–G823) we conclude that: (1) carbachol, CCK-8, gastrin and histamine increase parietal cell [Ca 2+] i initially by release of Ca 2+ from the same intracellular store(s); (2) the release of [Ca 2+] i in response to carbachol and CCK-8 in both chief and parietal cells appear to be mediated by IP 3; however, other mechanisms may be involved in histamine-induced release of parietal cell Ca 2+ i.