A. Loiseau et al., POTASSIUM-TRANSPORT IN OPOSSUM KIDNEY-CELLS - EFFECTS OF NA-SELECTIVEAND K-SELECTIVE IONIZABLE CRYPTANDS, AND OF VALINOMYCIN, FCCP AND NYSTATIN, Biochimica et biophysica acta. Biomembranes, 1330(1), 1997, pp. 39-49
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.