AJP - Gastrointestinal and Liver Physiology, Vol 261, Issue 1 92-103, Copyright © 1991 by American Physiological Society
Low doses of ethanol have Ca2+ ionophore-like effects on apical membrane potential of in vitro Necturus antrum
M. J. Rutten and C. D. Moore
Veterans Administration Medical Center Research Service, Kansas City, Missouri 64128.
The effects of low doses of luminal ethanol on the amiloride-sensitive
apical membrane potential of Necturus antral mucosa were studied using
conventional microelectrode techniques. Luminal ethanol (0.250-4.0%
vol/vol) caused a dose-dependent hyperpolarization of the apical membrane
potential (Vmc), an increase in transepithelial resistance (Rt) and
resistance ratio (Ra/Rb), and a decrease in transepithelial potential
(Vms). Luminal amiloride (100 microM) to 4% ethanol-treated antra did not
cause any additional hyperpolarization of Vmc. Compared with luminal 2%
ethanol-Ringer, an equivalent osmotic mannitol solution depolarized Vmc and
basolateral potential (Vcs), decreased Rt and Ra/Rb, and increased Vms. A
single dose of 0.50% ethanol attenuated the effects of a second 2% ethanol
exposure on Vmc. No change in periodic acid-Schiff (PAS)-positive mucous
granule content could be found between control and 2% ethanol-treated
antra. The Ca2+ ionophores A23187 or ionomycin (0.25-5.0 microM) dose
dependently hyperpolarized the Vmc and Vcs, increased Rt and Ra/Rb, and
decreased Vms. Luminal Ca(2+)-free Ringer had no effect on luminal 2.00%
ethanol-induced changes in membrane potentials or resistances. Pretreatment
with BAPTA blocked by approximately 70 and 55% the Vmc hyperpolarization of
2 and 4% ethanol, respectively. Pretreatment with ruthenium red (10-50
microM) also dose dependently reduced the 2% ethanol-induced changes in
Vmc. The data indicate that 1) low doses of luminal ethanol and Ca2+
ionophores have similar effects on Necturus gastric antral membrane
potentials and resistances, 2) ethanol-induced hyperpolarizations of the
Vmc are partially mediated through an alteration in intracellular Ca2+, and
3) low doses of luminal ethanol do not cause the release of antral
epithelial mucous granules at the time when significant changes are
occurring in the Vmc.
