Dog red blood cells exhibit a Ca-stimulated increase in K permeability in the absence of (Na,K)ATPase activity

The temperature dependence of passive potassium permeability in mammalian erythrocytes

The effect of temperature on the "passive" permeability of mammalian plasma membranes to K+, measured as the residual flux in the presence of ouabain and bumetanide, was investigated in erythrocytes of several species. Without Ca2+ in the medium, only human red cells demonstrated the "paradoxical" rise in passive flux at low temperature (i.e., below 12 degrees C) seen by other workers. In the other species no such effect was apparent; K+ influx decreased progressively with cooling down to 0 degree C. Below 18.5 degrees C the apparent energy of activation (Ea) was very low--close to that for free diffusion in water--for red cells of all species except human. Above 18.5 degrees C the Ea was much greater and was also more variable amongst the red cells of the species chosen. Neither the inhibitors used nor cell volume changes during incubation accounted for the absence of the paradoxical effect in the species studied here. A rise in permeation of K+ with cooling can, however, be produced by the addition of Ca2+ to the medium, probably by activation of the Ca2+-sensitive K+ channel. This effect would account for previous reports of a paradoxical effect in dog and rat erythrocytes.

Passive K+-Cl- fluxes in low-K+ sheep erythrocytes: modulation by A23187 and bivalent cations

A fraction of the ouabain-resistant (OR) K+ flux of low-K+ (LK) sheep erythrocytes is Cl- dependent (K+-Cl- transport) and is activated reversibly by cell swelling or irreversibly by treatment with N-ethylmaleimide (NEM). The effect of the ionophore A23187 plus bivalent cations (Me2+) or ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) was studied on K+-Cl- transport in control or NEM-treated LK cells. The following observations were made. 1) A23187 (6 microM), at a hematocrit of 10% (vol/vol) and in the presence of 1 mM EGTA, activated severalfold OR K+-Cl- transport in shrunken or swollen cells but failed to stimulate further K+-Cl- flux in NEM-treated cells. 2) In the absence of EGTA, but at very low external Ca2+ concentrations [( Ca2+]o = 10(-7) M), A23187 stimulated OR K+-Cl- flux in controls less than with EGTA and inhibited it slightly in NEM-treated cells. 3) When [Ca2+]o was raised to 10(-3) M, an almost complete inhibition of OR K+-Cl- fluxes occurred in shrunken, swollen, or NEM-treated cells. 4) Other Me2+ inhibited OR K+-Cl- flux in the presence of A23187 in the following order of decreasing potency: Mn2+ much greater than Ca2+ greater than Mg2+ greater than Sr2+ much much greater than Ba2+. 5) Stimulation of OR K+-Cl- flux by A23187 +/- EGTA and inhibition by A23187 + Ca2+ were reversible and did not alter significantly cellular ATP. 6) The stimulatory effect of A23187 plus EGTA, perhaps by Me2+ removal, on K+-Cl- flux and its inhibition by Ca2+ were reversibly abolished in metabolically depleted cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of A23187 and Ca2+ on volume- and thiol-stimulated, ouabain-resistant K+C1- fluxes in low K+ fluxes in low K+ sheep erythrocytes

Ouabain-resistant (OR), C1- -dependent K+ (K+C1-) transport measured by Rb+ influx in isosmotic and anisosmotic media was stimulated by the Ca2+ ionophore A23187 and EGTA (ethylene-glycol-tetracetic acid) in low K+ (LK) but not in high K+ (HK) sheep red cells. Increasing external Ca2+ concentrations, [Ca2+]o, from about 10(-7) to 10(-3)M in presence of A23187 and in absence of EGTA inhibited OR Rb+ influx, in LK red cells osmotically shrunken or swollen as well as treated with the thiol reagent N-ethylmaleimide (NEM). Hence the volume- and the NEM-stimulated K+C1- transport system in LK cells can be experimentally modulated by cellular Ca2+ or other Me2+, which may interact with sites on the K+C1- transporter under the control of membrane sulfhydryl (SH) groups.

Ca-induced K transport in human red blood cell ghosts containing arsenazo III. Transmembrane interactions of Na, K, and Ca and the relationship to the functioning Na-K pump

Increasing free intracellular Ca (Cai) from less than 0.1 microM to 10 microM by means of A23187 activated Ca-stimulated K transport and inhibited the Na-K pump in resealed human red cell ghosts. These ghosts contained 2 mM ATP, which was maintained by a regenerating system, and arsenazo III to measure Cai. Ca-stimulated K transport was activated 50% at 2-3 microM free Cai and the Na-K pump was inhibited 50% by 5-10 microM free Cai. Free Cai from 1 to 8 microM stimulated K efflux before it inhibited the Na-K pump, dissociating the effect of Ca on the two systems. 3 microM trifluoperazine inhibited Ca-stimulated K efflux and 0.5 mM quinidine reduced Na-K pumping by 50%. In other studies, incubating fresh intact cells in solutions containing Ca and 0.5 microM A23187 caused the cells to lose K heterogeneously. Under the same conditions, increasing A23187 to 10 microM initiated a homogeneous loss of K. In ATP-deficient ghosts containing Cai equilibrated with A23187, K transport was activated at the same free Cai as in the ghosts containing 2 mM ATP. Neither Cao nor the presence of an inward Ca gradient altered the effect of free Cai on the permeability to K. In these ghosts, transmembrane interactions of Na and K influenced the rate of Ca-stimulated K efflux independent of Na- and K-induced changes in free Cai or sensitivity to Cai. At constant free Cai, increasing Ko from 0.1 to 3 mM stimulated K efflux, whereas further increasing Ko inhibited it. Increasing Nai at constant Ki and free Cai markedly decreased the rate of efflux at 2 mM Ko, but had no effect when Ko was greater than or equal to 20 mM. These transmembrane interactions indicate that the mechanism underlying Ca-stimulated K transport is mediated. Since these interactions from either side of the membrane are independent of free Cai, activation of the transport mechanism by Cai must be at a site that is independent of those responsible for the interaction of Na and K. In the presence of A23187, this activating site is half-maximally stimulated by approximately 2 microM free Ca and is not influenced by the concentration of ATP. The partial inhibition of Ca-stimulated K efflux by trifluoperazine in ghosts containing ATP suggests that calmodulin could be involved in the activation of K transport by Cai.(ABSTRACT TRUNCATED AT 400 WORDS)

Hemolytic action of potassium salts on dog red blood cells

Recent demonstrations of chloride-associated passive potassium movements in red blood cells of humans, ducks, sheep, and toadfish prompted a reinvestigation of potassium permeability in dog red blood cells. Early observations of Davson (J. Physiol. London 101:265-283, 1942) had shown that replacement of chloride by nitrate and thiocyanate caused a greatly increased rate of potassium flux across the dog red cell membrane. This finding seemed at variance with results in other species in which chloride replacement caused a fall in potassium flux. The present data indicate that passive potassium movements in swollen dog red blood cells are chloride dependent and furosemide sensitive, as shown for the cells of other species. Davson's findings were demonstrated to be due to the inclusion of small quantities of calcium in the medium under circumstances that favored calcium entry into the cells, thus opening the calcium-activated potassium channel described by Gardos (Curr. Top. Membr. Transp. 10:217-277, 1978 and Nature London 279:248-250, 1979). Potassium movements through the latter channel were stimulated when chloride was replaced by more permeant anions, such as nitrate and thiocyanate, which also increased the rate of net potassium movements in valinomycin-treated cells.

Plasma membrane nadh dehydrogenase and Ca2+-dependent potassium transport in erythrocytes of several animal species

Ca2+-dependent K+ transport and plasma membrane NADH dehydrogenase activities have been studied in several 'high-K+' (human, rabbit and guinea pig) and 'low-K+' (dog, cat and sheep) erythrocytes. All the species except sheep showed Ca2+-dependent K+ transport. NADH-ferricyanide reductase was detected in all the species and showed positive correlation with the flavin contents of the membranes. NADH-cytochrome c reductase was very low or absent in dog, sheep and guinea pig membranes. No correlation was found between NADH dehydrogenase and Ca2+-dependent K+ channel activities in the species studied. Nor were any of the above activities correlated with (Na+ + K+)-ATPase activity.