Anion exchange in oxyntic cell apical membrane: Relationship to thiocyanate inhibition of acid secretion

The effects of SCN^- on H⁺-accumulation by inside-out gastric vesicles derived from the apical membrane of secreting oxyntic cells are reported. SCN^- inhibited the formation of pH gradients in Cl^- and isethionate media. In Cl^-, the concentration of SCN^- required to achieve a certain degree of inhibition of H⁺ uptake (or dissipation of preformed gradients) was increased with the increase in Cl^- concentration, indicating some competitive phenomena between these anions. Comparison of the rates of dissipation of similar pH gradients achieved in Cl^-vs. isethionate suggested the existence of a fast Cl^-/SCN^- exchange. In addition, direct isotopic fluxes confirmed the existence of rapid anion exchange and K-salt transport for both Cl^- and SCN^-. The rates of anion-exchange and K-salt transport were of similar magnitude, and the rates for SCN^- in either countertransport against Cl^- or cotransport with K⁺ were twice as fast as the equivalent values for Cl^-. These mediated pathways in the apical membrane provide the possible means for rapid access of SCN^- to the acidic canalicular spaces of the oxyntic cell that is implicit in recent proposals to explain SCN^- inhibition of gastric HCl secretion.