Calcium-potassium-stimulated net potassium efflux from human erythrocyte ghosts

Abstract

In the presence of 8 mM external Ca++, the K+ permeability of human red cell ghosts increases provided K+ is also present in the medium. This increase does not represent K+/K+ exchange but a stimulation of net K+ efflux. The stimulation is half-maximal at 0.7 +/- 0.15 mM (n=5). At concentrations above 4.0 mM, external K+ inhibits net K+ efflux. Similar stimulatory and inhibitory effects of external K were also observed in intact cells after exposure to Pb++ or to Ca++ in the presence of fluoride, iodoacetate plus adenosine, or propranolol, suggesting that a common K+ -activated K+ -specific transfer system may be involved under all of these various circumstances. Internal K+ also stimulates net K+ efflux from ghosts, but it is uncertain whether internal K+ is an absolute requirement for the K+ permeability increase. In contrast to external Na+ which slightly stimulates K+ efflux, internal Na+ inhibits. The inhibition by internal Na+ is abolished by sufficiently high concentrations of external K+, showing that K+ binding to the outer membrane surface and Na+ binding to the internal surface are mutually interdependent. In red cell ghosts the Ca++ -K+ -stimulated net K+ efflux increases with increasing pH until a plateau is reached between pH 7.2 and 8.0. In fluoride-poisoned intact cells, the Ca++-K+ stimulated flux passes through a maximum around pH 6.8. Neither internal nor external Mg++ interferes with the combined effects of Ca++ and K+. Similarly, external EDTA has no influence at concentrations which are far lower than the Ca++ concentration required to produce a maximal response. In contrast, low concentrations of internal EDTA prevent the permeability change.

Membrane potentials associated with Ca-induced K conductance in human red blood cells: Studies with a fluorescent oxonol dye, WW 781

“…8 are consistent with previous descriptions of Na activation of K efflux (Knauf et al 1975;Hoffman & Blum, 1977), and activation of Ca-dependent K efflux by Ko has been studied in ATP-depleted cells (Kregenow & Hoffman, 1972;Hoffman & Blum, 1977) and in red cell ghosts (Knauf et al, 1975;Simons, 1979;Heinz & Passow, 1980). The dependence on Ko illustrated by the results in Fig.…”

“…This stimulation of efflux by WW 781 is problematical for a quantitative analysis correlating fluxes and voltages. The inhibitory effect of K o on ~ contrasts with the stimulatory effect of K o on valinomycin-mediated K effiux (Hunter, 1977;Wieth & Tosteson, 1979), and agrees with previous studies of the Gardos effect in ATP-depleted cells (Blum & Hoffman, 1971;Kregenow & Hoffman, 1972;Hoffman & Blum, 1977) as well as in ghosts (Knauf et al, 1975;Heinz & Passow, 1980).…”

“…The study of K activation kinetics with tracer fluxes involves complications including irreversible inactivation at low Ko, time-dependent changes in rate constants, nonlinearities due to altered internal ionic concentrations, changes in cell volume, and possible cellular heterogeneity (Knauf et al, 1975;Heinz & Passow, 1980). Nevertheless, we measured initial unidirectional rates of Ca-induced Rb efflux at varied [K]o, using 86Rb as an economical tracer for K, in order to ascertain the extent to which WW 781 might itself influence the transport kinetics.…”

Electrophysiology of a clonal osteoblast-like cell line: Evidence for the existence of a Ca2+-activated K+ conductance

“…In these experiments we manipulated the Na + and K + chemical potential gradients by varying the extracellular Na + and K + concentrations. However, it has been shown for erythrocytes that the CaZ+-activated K + permeability is sensitive to the concentration of extracellular K + (Knauf et al, 1975). Recent studies have shown also that in other cell types, CaZ+-activated K + channels are voltage sensitive (Gorman & Thomas, 1980;Hermann & Hartung, 1982b;Barrett, Magleby & Pallotta, 1982).…”

Membrane sidedness and the interaction of H+ and K+ on Ca2(+)-activated K+ transport in human red blood cells.

“…Another possible consequence of Em effects on Gardos channel activity concerns the relationship between K+ effiux and K+. It has been reported (12, [36][37][38][39]) that activation of Ca2+-dependent K+ transport is biphasic, reaching peak activity at 2-3 mM K+ and then falling off as K+ is increased further. This is the situation in the absence of DIDS whether the principal anion is Cl-or SOt-.…”