Differential effects of gtp[gamma]s on acid and pepsinogen secretion by permeable gastric glands. Miller, M. D., and S. J. Hersey. Department of Physiology, Emory University, Atlanta, GA 30322
APStracts 3:0007G, 1996.
Gastric glands isolated from rabbit stomach were permeabilized with Staphylococcus aureus [alpha]-toxin. Acid secretion by parietal cells, as measured by the accumulation of weak base, was inhibited by incubation with [alpha]-toxin but could be restored by addition of exogenous ATP (1 mM). The permeable glands were found to retain acid secretory responses to receptor-linked secretagogues, histamine and carbachol, as well as to intracellular mediators, forskolin and 8-Br -cyclic AMP, indicating the presence of intact, functional intracellular coupling mechanisms. Both basal and stimulated acid secretion by the permeable glands was blocked by the Mg chelator, CDTA (5 mM), whereas CDTA had no effect on non-permeabilized glands. These results are interpreted to show that [alpha]-toxin permeabilizes parietal cells to moderate sized molecules without causing a loss of critical intracellular components. The acid secretory responses to histamine and carbachol persisted in media containing low (&LT50 nM) levels of free Ca2+ buffered by BAPTA (0.5 mM) indicating that changes in bulk calcium are not required for these responses. Inclusion of the nonhydrolysable analogue of GTP, GTP[gamma]S (100 [mu]M), resulted in inhibition of spontaneous acid secretion, blocked responses to all agents tested, and inhibited stimulated acid secretion. GTP[gamma]S had no effect on non -permeabilized glands. No effects on acid secretion by either permeable or non-permeable glands were observed with GTP, GDP or GDP[beta]S. GTP[gamma]S had no effect on proton gradient formation by gastric membrane vesicles showing that it does not inhibit the gastric H,K ATPase directly. These results are interpreted to show that GTP[gamma]S interacts at a post-receptor site to inhibit or reverse a critical step in stimulus-secretion coupling in parietal cells. In contrast to the effect on parietal cells, GTP[gamma]S was found to stimulate pepsinogen secretion by [alpha]-toxin permeabilized chief cells. The differential effects of GTP[gamma]S on acid and pepsinogen secretions suggests unique roles for GTP binding proteins in these two secretory processes. The use of [alpha]-toxin permeabilized gastric glands should prove useful in defining the stimulus-secretion coupling mechanisms involved in both acid and pepsinogen secretions. 

Received 16 October 1995; accepted in final form 12 December
1995.
APS Manuscript Number G452-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96