Stimulation of gastric acid secretion by camp in a novel -toxin
-permeabilized gland model.
Yao, Xuebiao, Sherif Karam, Marlon Ramilo, Qinfen Rong, Alan
Thibodeau, and John G. Forte.
Department of Molecular and Cell Biology, University of California,
Berkeley, CA 94720, USA and Department of Anatomy, Faculty of
Medicine, University of Kuwait, Safat, 13110, Kuwait
APStracts 3:0048C, 1996.
It is generally believed that histamine-stimulated gastric acid
secretion involves a transient elevation of intracellular Ca2+ and
the cAMP-dependent protein kinase (PKA) cascade through
phosphorylation, whose actions ultimately effect the fusion of H+,K+
-ATPase-containing vesicles to the apical plasma membrane of parietal
cells. To dissect the signaling events underlying gastric acid
secretion, we have developed a permeabilized gastric gland model
using Staphylococcus [alpha]-toxin. The advantage of this model is
its ability to retain cytosolic components that are required for the
secretory machinery. Here we show that acid secretion in [alpha]
-toxin-permeabilized glands is a cAMP-dependent process, reaching a
maximal stimulation at 100 [mu]M cAMP. The cAMP-elicited acid
secretion, as monitored by the accumulation of the weak base
aminopyrine (AP), required functional mitochondria or exogenously
supplied ATP. Maximal stimulation elicited by cAMP for AP uptake by
permeabilized glands was 51% to 85% of intact glands. Moreover,
secretory activity was potentiated by 0.1 mM ATP. The recruitment of
H,K-ATPase-rich tubulovesicles into the apical plasma membrane was
measured using biochemical and morphological assays, thus validating
the cell activation processes in response to cAMP. Taking advantage
of this permeabilized model, [gamma]32P-ATP was used to directly
phosphorylate target proteins. A number of proteins were found whose
phosphorylation/ dephosphorylation is specifically modulated by cAMP.
These studies establish the first permeabilized gland model in which
resting/secreting transition can be triggered, and show that cAMP
-mediated phosphorylation is correlated with secretory activity.
Received 27 November 1995; accepted in final form 5 January 1996.
APS Manuscript Number C705-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96