Properties of gastric antrum. III. Selectivity and modification of shunt conductance

The permselectivity of the paracellular pathway of amphibian (Necturus and bullfrog) antrum was investigated with respect to intracationic selectivity and the K+ and Cl- permeability ratio as a function of mucosal pH. The intracationic selectivity sequence was Rb+ greater than K+ greater than Cs+ greater than Na+ greater than Li+. Both antra showed weak cationic selectivity at pH 7.4, and at pH 4.4 for bullfrog and pH 3.0 for Necturus, the ratio Pk+/P Cl- was unity. At lower mucosal pH the tissues were anion selective. Treatment of the tissue with a water-soluble carbodiimide enhanced anion selectivity at higher pH; carbenoxolone, a weak acid, resulted in maintained cation selectivity at lower pH. These data suggest that carboxyl groups play a role in determining shunt selectivity; the increase in anion selectivity below pH 2.0 suggests that phosphate or sulfate groups could also be involved.