Potassium transport in opossum kidney cells: Effects of Na-selective and K-selective ionizable cryptands, and of valinomycin, FCCP and nystatin

Abstract

The effects of two ionizable cryptands, the Na-selective (221)C 10 and the K-selective (222)C 10, and of valinomycin, FCCP and nystatin on K + fluxes in opossum kidney (OK) cells have been quantified. The Na,K-ATPase (ouabain-sensitive 86Rb influx) was stimulated by nystatin (≥20%), and inhibited by the other ionophores (50–80%), by barium (K-channel blocker) (61%) and by amiloride (Na entry blocker) (34%). The V max of the Na,K-ATPase phosphatase activity was unmodified by the ionophores, indicating the absence of direct interaction with the enzyme. The ATPi content was unmodified by the inhibitors and nystatin, but was lowered by (221)C 10 (47%), (222)C 10 (75%), valinomycin (72%) and FCCP (88%). Amiloride was found to partially remove the inhibition caused by (222)C 10 (51%) and valinomycin (49%). Rb efflux was stimulated by nystatin (32%), unmodified by valinomycin, and was inhibited by (221)C 10 (19%), (222)C 10 (19%) and FCCP (10%). Barium (39%) and amiloride (32%) inhibited this efflux and, in their presence, the nystatin effect persisted, whereas that of the other ionophores vanished. At pH 6.4, the Rb efflux decreased by 14% of its value at pH 7.4, with no additional inhibition by cryptands. Cryptands are shown to inhibit the pH-sensitive K +-conductance, probably by inducing a K +–H + exchange at the plasma membrane, and by uncoupling oxidative phosphorylation by inducing the entry of K + and H + (and possibly Ca 2+) ions into the mitochondria.