AJP - Gastrointestinal and Liver Physiology, Vol 256, Issue 4 798-G807, Copyright © 1989 by American Physiological Society
Effects of cations and pH on apical membrane potential of in vitro Necturus antrum
M. J. Rutten, R. Delcore, D. I. Soybel, C. D. Moore and L. Y. Cheung
Veterans Administration Medical Center, Medical Research Service, Kansas City, Missouri 64128.
The surface epithelial cells of the gastric mucosa transport Na+ from lumen
to serosa. The first step in this process is the entry of Na+ through an
amiloride-sensitive Na+ channel at the apical membrane. The exact
function(s) of this Na+ transport are unknown, but it has been suggested
that it might help the stomach to withstand an acid load. The present study
was undertaken to examine the effects of low luminal pH and the alkali
cations Li+, K+, Rb+, and Cs+ on the amiloride-sensitive Na+ permeability
of the apical membrane of Necturus antral cells by measuring the changes in
apical membrane voltage (Vmc) using conventional microelectrode techniques.
Isosmolar replacement of luminal NaCl (pH 7.25) with LiCl caused a
depolarization of the Vmc, a decrease in transepithelial resistance (Rt),
and an increase in the transepithelial potential (Vmc), whereas replacement
with KCl, RbCl, or CsCl caused a hyperpolarization of the Vmc, an increase
in Rt, and a decrease in the Vmc. Luminal acidification from pH 7.25 to pH
3.00 caused very similar changes with all the cation solutions tested,
hyperpolarizing the Vmc, increasing Rt, and reducing the Vmc to near 0 mV.
Acidification of the luminal NaCl solution from pH 7.25 to pH 2.00 caused a
progressive hyperpolarization of the Vmc similar to the effects seen with
luminal amiloride (10(-4) M) in pH 7.25 NaCl solutions or luminal Na+-free
(N-methyl-D-glucamine) Ringer at pH 7.25. These results demonstrate that 1)
of the cations tested only Li+ can substitute for Na+ in maintaining the
Vmc, and 2) external H ions (low luminal pH) block cation permeability of
the apical membrane.
