AJP - Gastrointestinal and Liver Physiology, Vol 250, Issue 6 765-G772, Copyright © 1986 by American Physiological Society
Potassium selectivity of frog gastric luminal membrane
D. K. Kasbekar
Transmural potential difference (PD) and resistance (R) changes after
luminal or serosal instillation of K+ were determined under various
conditions in chambered preparations of frog gastric mucosae. Potassium
selectivity of the luminal membrane is indicated by the rapid reversal of
the inverted PD of mucosae bathed in NaCl-free, choline sulfate
(Ch2SO4)-Ringer on the serosal side and unbuffered hypertonic Ch2SO4
solution on the luminal side on luminal K+ instillation. The delta PD
responses are significantly attenuated, however, in histamine-stimulated
mucosae bathed in hypotonic or in burimamide-inhibited mucosae bathed in
hyper- and hypotonic luminal media, which suggests that the K+ selectivity
of the luminal membrane resides largely in the tubular cell apical
membrane. Imposing a serosal-to-luminal transmucosal K+ gradient in both
histamine-stimulated and omeprazole-inhibited mucosae also reversed the
normal orientation of PD but not in those inhibited with burimamide. In the
latter, the PD inversion was attenuated but maintained its normal
orientation. These data suggest that burimamide, but not omeprazole, acts
by blocking luminal membrane K+ conductance. The inverted PD in mucosae
bathed in Cl-free media may thus be due partially or fully to K+ diffusion
driven by the cell-to-lumen K+ gradient via the luminal K+ conductance
pathway. These findings have implications for the controversy surrounding
the postulated electrogenicity of the gastric proton pump.
