Chloride-activated passive potassium transport in human erythrocytes.

Abstract

Passive K+ transport in human erythrocytes (defined as ouabain-insensitive transport) was inhibited 70% by replacement of Cl-by several permeant monovalent anions.The VmaX of Cl--dependent K+ influx was 1.14 mmol-liter-lhr-1; its apparent Km for K+ was 4.7 mM. There was a much smaller commnent of Na+ influx dependent on Cl- (Vm..x, 0.23 mmol-liter-hr-1). Furosemide and other inhibitors of Cltransport inhibited passive K+ transport to the same extent as replacement of Cl-, but 4-acetamido4'-isothiocyanostilbene-2,2'-disulfonic acid, a specific inhibitor of anion exchange in erythrocytes, was ineffective. The Cl--dependent K+ transport, which may be K+/C1-cotransport, could reflect a mechanism for regulating cell volume.Human erythrocytes have at least four transport systems for K+ to cross the membrane: the Na+/K+ pump (1), the Ca2+-activated transport system (or Gardos effect) (2), the Na+/K+ cotransport system (3-5), and a nonspecific electrodiffusional leak (6). In sheep erythrocytes there is an additional passive K+ transport system that is sensitive to changes in cell volume: K+ fluxes increase in swollen cells and decrease in shrunken cells. This K+ transport system requires the presence of chloride for its operation (7). In the present paper we report the Cl-dependence of passive K+ transport in human erythrocytes (passive transport taken to mean a process not inhibited by ouabain). We show the kinetics of the Cl--activated influx with regard to extracellular concentrations of K+ and Cl-, [K]o and [Cl]0. Passive Na+ influx was also dependent on Cl-, but the maximal velocity was one-fifth that for K+. Finally, we present results on pharmacological agents and Cl--activated K+ influx. Of particular interest is furosemide which, in erythrocytes, inhibits both Cl-transport (8) and Na+/K+ cotransport (5).MATERIALS AND METHODS Cells. Blood was drawn by venipuncture from healthy adult donors. The erythrocytes were washed three times in an isotonic saline solution by centrifugation and resuspension. The saline solution contained 150 mM NaCI, 5 mM glucose, 10 mM Hepes at pH 7.5 (adjusted at 20°C with NaOH). In all experiments the cells used had been obtained the same day.Chloride Replacement. In order to study the effects of varying [Cl]0, we equilibrated cells in media with various permeant anions at 150 mM substituted for Cl-in the isotonic saline. The cells were first washed in a medium with the same composition as the isotonic saline (except for the substituted anion) and incubated at 37°C for 30 min. They were then washed again, incubated another 30 min, and finally washed three more times.Fluxes. Unidirectional influxes were measured as described (9) with 24Na, 22Na, or 86Rb (the latter as a tracer for K+). The incubations with the tracer were for 30 min. The Cl-added with the tracer was ignored (final concentration z1 AM). The method used for unidirectional K+ efflux has been described (10); 42K was used as a tracer. Na+ efflux was measured by the same method. All fluxes are expressed as mmol per...

Acetylcholine‐evoked potassium release in the mouse pancreas.

“…This fits exactly the anion requirements of Na+-K+-2Cl-cotransport in red cells and cultured HeLa cells (Chipperfield, 1981;Aiton & Simmons, 1983) as well as the anion requirements of salivary fluid secretion (Lundberg, 1957) whereas with regard to the C1--HCO3-exchanger it has been known for a long time that NO3-is an equally good exchange partner for Cl-as Cl-itself while Br-and l-are less efficient (Gunn, Wieth & Tosteson, 1975). Our findings presented in Figs. 3-6 are therefore most easily interpreted by assuming the existence of linked Na+, K+ and Cl-movements through a Na+-K+-2Cl-co-transporter (Aiton, Chipperfield, Lamb, Ogden & Simmons, 1981;Dunham & Ellory, 1981;Chipperfield, 1980Chipperfield, ,1981Dunham, Stewart & Ellory, 1980;Greger & Schlatter, 1981,1984Haas, Schmidt & McManus, 1982;Hannafin, Kinne-Safran, Friedman & Kinne, 1983). The results in the mouse pancreas can most easily be explained by assuming that the Na+-K+-2Cl-co-transport moves the ions from the cell interior to the exterior (Singh, 1984a), i.e.…”

Sodium-potassium pump, ion fluxes, and cellular dehydration in sickle cell anemia.

“…The portion ofssRb uptake that is insensitive to ouabain and inhibited by furosemide is mediated through Na,K-cotransport present in human red blood cells (15,16). To evaluate Na,K-pump-independent Rb/K uptake further, triplicate samples of red cells were incubated with 0.1 mM ouabain alone, or both ouabain and I mM furosemide, under experimental conditions analogous to those described above.…”

Disruption of erythroid K-Cl cotransporters alters erythrocyte volume and partially rescues erythrocyte dehydration in SAD mice

“…K-Cl cotransporters (KCCs) mediate electroneutral symport of K + and Cl -ions across the plasma membrane that is mostly outwardly directed and was originally described in rbc (1)(2)(3). K-Cl cotransport is mediated in a wide range of tissues by the polypeptide products of the 4 homologous SLC12 cation cotransporter superfamily genes SLC12A4/KCC1, SLC12A5/KCC2, SLC12A6/KCC3, and SLC12A7/KCC4 (4).…”