POTASSIUM-TRANSPORT IN OPOSSUM KIDNEY-CELLS - EFFECTS OF NA-SELECTIVEAND K-SELECTIVE IONIZABLE CRYPTANDS, AND OF VALINOMYCIN, FCCP AND NYSTATIN

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-A TPase (ouabain-sensitive Rb-86 influx) was stimulated by nystatin (gre ater than or equal to 20%), and inhibited by the other ionophores (50- 80%), by barium (K-channel blocker) (61%) and by amiloride (Na entry b locker) (34%). The V-max of the Na,K-ATPase phosphatase activity was u nmodified by the ionophores, indicating the absence of direct interact ion 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%), va linomycin (72%) and FCCP (88%). Amiloride was found to partially remov e the inhibition caused by (222)C-10 (51%) and valinomycin (49%). Rb e fflux was stimulated by nystatin (32%), unmodified by valinomycin, and was inhibited by (221)C-10 (19%), (222)C-10 (19%) and FCCP (10%). Bar ium (39%) and amiloride (32%) inhibited this efflux and, in their pres ence, the nystatin effect persisted, whereas that of the other ionopho res vanished. At pH 6.4, the Rb efflux decreased by 14% of its value a t pH 7.4, with no additional inhibition by cryptands. Cryptands are sh own to inhibit the pH-sensitive K+-conductance, probably by inducing a K+-H+ exchange at the plasma membrane, and by uncoupling oxidative ph osphorylation by inducing the entry of K+ and H+ (and possibly Ca2+) i ons into the mitochondria. (C) 1997 Elsevier Science B.V.