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

Summary

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.