La3+ and ph sensitivity of ca2+ entry and intracellular store
filling in gastric parietal cells.
Negulescu, Paul A., and Terry E. Machen.
Dept. of Molecular and Cell Biology, Division of Cell and
Developmental Biology, 231 LSA, University of California at Berkeley,
Berkeley, CA. 94720
APStracts 2:0119G, 1995.
The fluorescent Ca2+ indicator, fura-2, was used to measure cytosolic
free [Ca2+] (Ca2+i) in order to obtain information about relative
rates of Ca2+ influx into parietal cells during treatment with either
carbachol (a cholinergic agonist) or thapsigargin (TG, a Ca2+
mobilizing agent), or during reloading of the internal Ca2+ stores.
In Ca2+-containing solutions, carbachol-, TG-, and reloading
-stimulated Ca2+ entry exhibited nearly identical sensitivity to La3+
(Ki 10[mu]M) or low pH (pKi 7.0). In experiments using both
carbachol and TG, there was no additional increase in Ca2+i when TG
was added to carbachol-treated cells or when carbachol was added to
cells previously treated with TG. Thus, it is likely that a single
Ca2+ entry pathway serves a signaling function as well as playing a
role in refilling of the Ca2+ store during reloading. Because the
Ca2+ pathway is exquisitely sensitive to pH, and serosal pH increases
during stimulant-induced H secretion (which is activated by increases
in Ca2+i), this mechanism will exert positive feedback on parietal
cells in the intact stomach. If parietal cells were pretreated with
carbachol in Ca2+-free solutions, reloading was pH- and La3+
-independent, suggesting that Ca2+-containing solutions should be used
to determine the properties of the influx pathway.
Received 20 September 1993; accepted in final form 18 May 1995.
APS Manuscript Number G369-3.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.