Potassium selectivity of frog gastric luminal membrane
Kasbekar, D.K.
American Journal of Physiology 250(6 Pt 1): G765-G772
1986
ISSN/ISBN: 0002-9513 PMID: 2424319 Document Number: 282753
Transmural potential difference (PD) and resistance (R) changes after luminal or serosal instillation of K+ were estimated in different conditions in chambered preparations of frog gastric mucosae. Potassium selectivity of the luminal membrane was indicated by the rapid reversal of the inverted PD of mucosae bathed in NaCl-free, choline sulphate (Ch2SO4)-Ringer on the serosal side and unbuffered hypertonic Ch2SO4 solution on the luminal side on luminal K+ instillation. The Delta PD responses were significantly attenuated 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 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. The results suggest that burimamide, but not omeprazole, act by blocking luminal membrane K+ conductance. The inverted PD in mucosae bathed in Cl-free media may thus be due partly or fully to K+ diffusion driven by the cell-to-lumen K+ gradient via the luminal K+ conductance pathway. The findings have implications for the controversy surrounding the postulated electrogenicity of the gastric proton pump.