Stimulation of monovalent cation fluxes by electron donors in the human red cell membrane

Oxidation-induced calcium-dependent dehydration of normal human red blood cells

Phenazine-methosulphate (PMS) is a strong oxidant that induces reactive oxygen species (ROS) formation in cells. Though it has been shown that PMS increases the red blood cell (RBC) membrane permeability to K(+), the hypotheses on the mechanism of PMS-induced effects are contradictory and there are no data on volume changes induced by this oxidant. Therefore, the influence of the PMS + ascorbate oxidative system on the volume of normal human RBCs was studied. In a Ca(2 + )-containing medium, PMS + ascorbate caused dehydration (shrinking) of RBCs judged by: (1) changes in the density and osmotic resistance distributions of RBCs, and (2) a decrease in their low-angle scattering assessed by FACS analysis. The dehydration resulted from activation of the Gardos channels, was PMS and ascorbate concentration-dependent, was associated with broadening of the density and osmotic resistance distributions of the RBCs, and decreased in the presence of the taxifolin and rutin antioxidants. These findings contribute to a better understanding of the physiology and pathology of oxidatively-modified RBCs and may be of practical significance in estimating the antioxidant activity of various substances.

Modulation of Gardos channel activity by oxidants and oxygen tension: effects of 1-chloro-2,4-dinitrobenzene and phenazine methosulphate

We compare the effects of 1-chloro-2,4-dinitrobenzene (CDNB) and phenazine methosulphate (PMS) on Gardos channel activity in normal human red cells. Both stimulate channel activity, both are dependent on the presence of extracellular Ca2+, and neither is affected by inhibitors of protein (de)phosphorylation. Of the two, PMS has a considerably greater effect. In addition, a major difference is that whilst CDNB has a greater stimulatory effect in oxygenated cells, by contrast, PMS is more effective in deoxygenated cells. These actions are correlated with ca. 30% inhibition of the plasma membrane Ca2+ pump (PMCA) and an increased sensitivity of the Gardos channel to Ca2+ (EC50 falling to about 150 nM). These findings are important in understanding how oxidants alter red cell cation permeability and may be relevant to the abnormal permeability phenotype shown by deoxygenated sickle cells.

The effects of adriamycin and adriamycin complexes with transitional metals on Ca(2+)-dependent K+ channels of human erythrocytes

The influence of adriamycin (ADR) and ADR complexes with transitional metals Fe2+, Cu2+ and Co2+ on Ca(2+)-dependent K+ channels of human erythrocytes was investigated. We show that the anthracycline moiety of ADR increases Ca(2+)-dependent K+ efflux from erythrocytes, induced by low concentrations of propranolol, while the whole molecule of ADR has not any effect on Ca(2+)-dependent K+ channels, induced by propranolol or A23187 and on Pb(2+)-dependent K+ efflux. Ethidium bromide, verapamil and trifluoroperazine inhibited Ca(2+)-dependent K+ efflux, induced by high doses of propranolol. The anthracycline moiety of ADR is able to abolish blocking effect of ethidium bromide and verapamil, but does not influence the blocking effect of trifluoroperazine. We further show that ADR complexes with Fe2+, Cu2+ and Co2+ are potent inhibitors of Ca(2+)-dependent K+ efflux, induced by propranolol, but not of Pb(2+)-dependent K+ efflux. On the contrary, ADR-Fe3+ complex activates K(+)-permeability of human red blood cell. It is suggested that opposite effects of anthracycline moiety of ADR and ADR complexes with transitional metals on Ca(2+)-dependent K+ channels, induced by propranolol is due to their influence on the pathways of Ca2+ transport into cells, rather than their action directly on K+ channels.

Modulation of the Ca2+- or Pb2+-activated K+-selective channels in human red cells. II. Parallelisms to modulation of the activity of a membrane-bound oxidoreductase

Modulation of Ca2+-activable K+ permeability was compared with modulation of a membrane-bound oxidoreductase activity in human erythrocytes. Changes in the K+ permeability were monitored by flux measurements and single-channel recordings. The enzyme activity was detected by measuring reduction of ferricyanide. Pb2+, Atebrin and menadione had parallel effects on the channel protein and the enzyme. In contrast, propranolol stimulates K+ permeability, but is without effect on enzyme activity. The results demonstrate that the K+ channel and the enzyme are distinct membrane proteins but that the enzyme activity may influence channel gating.

Thiol-dependent K:Cl transport in sheep red cells: VIII. Activation through metabolically and chemically reversible oxidation by diamide

The sulfhydryl (SH) oxidant diamide activated in a concentration-dependent manner ouabain-resistant (OR), Cl-dependent K flux in both low potassium (LK) and high potassium (HK) sheep red cells as determined from the rate of zero-trans K efflux into media with Cl or Cl replaced by NO3 or methane sulfonate (CH3SO3). Diamide did not alter the OR Na efflux into choline Cl. The diamide effect on K efflux appeared after 80% of cellular glutathione (GSH) was oxidized to GSSG, its disulfide. The stimulation of K efflux was completely reversed during metabolic restitution of GSH, a process that depended on the length of exposure to and the concentration of diamide. The action of diamide on both the K:Cl transporter and GSH was also fully reversed by the reducing agent dithiothreitol (DTT). Diamide apparently oxidized the same SH groups alkylated by N-ethylmaleimide (NEM) (Lauf, P.K. 1983. J. Membrane Biol. 73:237-246). Like NEM, diamide activated K:Cl transport several-fold more in LK cells than in HK cells, and the effect on LK cells was partially inhibited by anti-L1, the allo-antibody known to inhibit OR K fluxes.

Magnitude of calcium influx required to induce dehydration of normal human red cells

Activation by [Ca2+]i of Ca2+-sensitive K+ channels has long been known to cause dehydration of red cells suspended in low-K, plasma-like media. However, the fundamental question of the extent to which Ca influx must be increased to trigger dense cell formation in conditions likely to arise in the circulation has not been established. We report here that in ionophore permeabilized red cells, increasing Ca influx above 0.7 mmol/litre cells per h induces the formation of subpopulations of dehydrated cells within 1-2 hours. The presence or absence of glycolytic substrates had little effect suggesting that ATP depletion was not large enough to significantly inhibit the pump within that period. Below maximal dehydrating Ca influxes of about 1.2 mmol/litre cells per h, the trend was for the fraction of dense cells formed to remain steady in time. As Ca influx was increased, both the rate of dense cell formation and the fraction of dense cells formed increased. These results are analyzed in relation to mechanisms and to possible states of increased Ca2+ permeability in physiological and physiopathological conditions.

Phenazine methosulfate induces a neurally-mediated contraction of the guinea-pig ileum

Phenazine methosulfate (PMS) and related phenazines are widely used in biochemistry and histochemistry and act as anti-bacterial agents, however, there is little information on their pharmacological actions. In the present paper the guinea-pig ileum was used as a model for studying the effects of PMS on nerve cells. PMS was found to contract intestinal muscle. This action appeared to be mediated by the activation of muscarinic receptors since it was blocked by atropine. Neostigmine potentiated the response to PMS. The nerve blocker tetrodotoxin prevented the effect of PMS and it is concluded that PMS causes the release of acetylcholine from nerve elements. The action of PMS on nerves is not mediated by nicotinic receptors. Receptors for serotonin, substance P or cholecystokinin also appear not to be involved. Of all the phenazines tested PMS was found to be the most potent and reversible.

Decrease of NADH in yeast cells by external ferricyanide reduction

Ferricyanide reduction catalyzed by vitamin K-3 was accompanied by the decrease in intracellular (NAD(P)H concentration of yeast cells, and the rate of ferricyanide reduction depended on intracellular concentration of NADH rather than NADPH. The addition of glucose to the cell suspensions enhanced both ferricyanide reduction and intracellular NADH concentration. The catalytic action of vitamin K-3 on ferricyanide reduction was observed in the presence of NADH and plasma membrane preparations. As the toxic action of vitamin K-3 on cell growth of yeast was enhanced by addition of ferricyanide, ferricyanide reduction catalyzed by vitamin K-3 may inhibit cell growth by decreasing intracellular NADH concentration.

Modulation of Ca2+-dependent K+ transport by modifications of the NAD+/NADH ratio in intact human red cells

The effects of variations of the NAD+/NADH quotient on the uptake of 86Rb by human red cells loaded by non-disruptive means with the chelator Benz2 and different amounts of 45Ca has been examined. The NAD+/NADH quotient was modified by the addition of pyruvate and/or lactate or xylitol. It was found that the uptake of 86Rb at a given intracellular Ca2+ concentrations was faster in the reduced state (lactate or xylitol added). Metabolic changes were associated with variations of the redox state. However, glycolitic intermediates did not significantly modify the apparent affinity for Ca2+ of the Ca2+-dependent K+ channel in one-step inside-out vesicles prepared from the erythrocyte membrane. Taken together, these results suggest that modifications of the cytoplasmic redox potential could modulate the sensitivity to Ca2+ of the Ca2+-dependent K+ channel in the human red cells under physiological conditions. This conclusion is consistent with previous findings in inside-out vesicles of human erythrocytes using artificial electron donors.

Effects of vanadate, menadione and menadione analogs on the Ca2+-activated K+ channels in human red cells. Possible relations to membrane-bound oxidoreductase activity

The modulation of the Ca2+- (or Pb2+-)activated K+ permeability in human erythrocytes by vanadate, menadione and chloro-substituted menadione analogs was investigated by measurements of K+ fluxes and single-channel currents. Vanadate and menadione stimulate the K+ permeability by increasing the probability of channel openings; the menadione analogs, on the other hand, inhibit the K+ permeability by increasing the probability of channel closings. The compounds used in these experiments also interact with oxidoreductases; it is demonstrated that menadione analogs in contrast to menadione strongly inhibit the membrane-bound dehydrogenase in the erythrocytes. Concentrations of Pb2+ above 10 mumol/l, but not of Ca2+, inhibit the enzyme activity as well as the K+ permeability. The parallel effects on dehydrogenase activity and the K+ channels suggest a direct relationship between these two systems in the membrane of erythrocytes.

Hyperpolarization of mouse skeletal muscle plasma membrane induced by extracellular NADH

Extracellularly applied NADH, but not NAD or NADPH, increases the resting membrane potential from -74.1 to -76.6 mV in freshly isolated muscles in the presence of K+ in the incubation medium and from -64.6 to -72.9 mV in muscles equilibrated for 4-6 h in a K+-free solution. The NADH-induced hyperpolarization is blocked by pretreatment of muscles with ouabain, and the inhibitors of plasma membrane NADH dehydrogenase (adriamycin, azide, PCMB, atebrine, DIDS and bleomycin). The effect of NADH is accompanied by the disappearance of NADH from the incubation medium and by decreased membrane resistance. We conclude that NADH hyperpolarization is due to the enhancement of passive membrane permeability, apparently for K+, which might result from the conformational changes in the plasma membrane during the NADH dehydrogenase reaction. The possibility is discussed that NADH dehydrogenase mediates transport of K+ out from the cell using a pathway connected with the transmembrane Na+/K+ pump.

Effects of electron donors on Ca2+-dependent K+ transport in one-step inside-out vesicles from the human erythrocyte membrane

The interactions between reducing agents and Ca2+ in the activation of Ca2+-dependent K+ transport have been studied in one-step inside-out vesicles. The artificial electron donor system ascorbate + phenazine methosulphate increases the apparent sensitivity to Ca2+ by about 5-times over control values (half activation constant, about 5 X 10(-8) M) while oxidized cytochrome c decreases the sensitivity to about 1/3 of the controls. Using redox buffers at a fixed pCa it is shown that the shift from the low to the high-affinity state can be accounted by the reduction of a membrane component accepting two electrons and with an apparent standard redox potential (pH 7.5) of 47 mV. The electrons can be transferred directly from reduced PMS or to oxidized cytochrome c, but not from ascorbate, NADH or reduced glutathione.

Interaction between propranolol and electron donors in altering the calcium ion-dependent potassium ion-permeability of the human red blood cell membrane

Both propranolol and the electron donors ascorbate plus phenazine methosulfate increase the K+-permeability of the red blood cell membrane. The present investigation examined whether these effects were additive. Contrary to expectations, propranolol added after electron donors sharply inhibited the K+ (86Rb) efflux induced by such donors, without forming new K4 channels analogous to those induced by propranolol in intact red blood cells. The inhibitory effect of propranolol may be due to generalized disturbances of membrane structures necessary for the functioning of the K+ channels organized in the presence of reducing agents. In contrast, the electron donors added after propranolol caused a further stimulation of the 86Rb loss from the propranolol-treated red cells. The combined effect of these drugs therefore depends on the order of their addition. The possible mechanism of their interaction is briefly discussed.

Properties of the Ca-activated K+ channel in pancreatic beta-cells

The existence of [Ca2+]i-activated K+-channels in the pancreatic beta-cell membrane is based in two observations: quinine inhibits K+-permeability and, increasing intracellular Ca2+ stimulates it. The changes in K+-permeability of the beta-cell have been monitored electrically by combining measurements of the dependence of the membrane potential on external K+ concentration and input resistance. The changes in the passive 42K and 86Rb efflux from the whole islet have been measured directly. Intracellular Ca2+ has been increased by various means, including increasing extracellular Ca2+, addition of the Ca2+-ionophore A23187 or noradrenaline and application of mitochondrial uncouplers and blockers. In addition to quinine, many other substances have been found to inhibit or modulate the [Ca2+]i-activated K+-channel. The most important of these is the natural stimulus for insulin secretion, glucose. Glucose may inhibit K+-permeability by lowering intracellular Ca2+. Glibenclamide, a hypoglycaemic sulphonylurea, is about 25 times more active than quinine in blocking the K+-channel in beta-cells. The methylxanthines, c-AMP, various calmodulin inhibitors and Ba2+ also inhibit K+-permeability. Genetically diabetic mice have been studied and show an alteration in the [Ca2+]i-activated K+-channel. It is concluded that the [Ca2+]i-activated K+-channel plays a major role in the normal function of the pancreatic beta-cell. The study of its properties should prove valuable for the understanding and treatment of diabetes.

Effects of redox agents on the Ca2+-activated K+ channel

The sensitivity to Ca2+ of the Ca2+-dependent K+ channel can be increased by the artificial electron donor system ascorbate + phenazine-methosulphate in a variety of animal cells. In the human erythrocyte the shift from the 'low' to the 'high-affinity' state seems to depend on the reduction of a membrane component accepting 2 electrons and with an standard redox potential (pH 7.5) of about 47 mV. The relevance of this redox modulation under physiological circumstances is unknown at the moment.

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.

A method for estimating free Ca within human red blood cells, with an application to the study of their Ca-dependent K permeability

Murphy, Coll, Rich and Williamson (J. Biol. Chem. 255:6600--6608, 1980) described a null-point method for estimating intracellular free Ca in liver cells. They used digitonin to lyse the cells in solutions of varying Ca concentration. This method has been adapted for use with human red cells. The values found are about 0.4 micron or micrometer Ca in fresh cells, and from 0.4 to 0.7 micron or micrometer Ca in blood-bank cells, at pH 7.2 and 37 degrees C. These are likely to be overestimates, and the errors and limitations of the method are discussed. Red cells may be loaded with Ca by metabolic depletion in Ca-containing solutions. Such cells have an elevated K permeability, and the relationships between free Ca, total Ca and K permeability were investigated, using 86Rb as a tracer for K. 86Rb flux studies show that the affinity of the K channel for Ca is the same in cells as in resealed ghosts where intracellular Ca can be controlled with Ca buffers, but the rate of tracer equilibration is 3-6 times faster in ghosts than in cells.

Ca2+-dependent K+ transport in the Ehrlich ascites tumor cell

The possible presence and properties of the Ca2+-dependent K+ channel have been investigated in the Ehrlich ascites tumor cell. The treatment with ionophore A23187 + CA2+, propranolol or the electron donor system ascorbate-phenazine methosulphate, all of which activate that transport system in the human erythrocyte, produces in the Ehrlich cell a net loss of K+ (balanced by the uptake of Na+) and a stimulation of both the influx and the efflux of 86Rb. These effects were antagonized by quinine, a known inhibitor of the Ca2+-dependent K+ channel in other cell systems, and by the addition of EGTA to the incubation medium. Ouabain did not have an inhibitory effect. These results suggests that the Ehrlich cell possesses a Ca2+-dependent K+ channel whose characteristics are similar to those described in other cell systems.

Effect of extracellular potassium on the loss of potassium from human red blood cells treated with propranolol

The Ca++-dependent propranolol-induced increase of K+ permeability of human red blood cells, well documented in previous studies, was found to depend on extracellular K+. This was shown by studying the passive transport of 86Rb and the loss of bulk cellular K+ in both K+-free and K+-containing media. The maximal effect of propranolol was achieved with 5-10 mM K+ in incubation media. The external K+ could be substituted with Tl+, but not with Na+. When added after propranolol, extracellular K+ failed to initiate the effect of propranolol on membrane permeability. The cell/medium distribution of permeant 204Tl showed that the propranolol-induced increase of K+ permeability did not result in considerable hyperpolarization of the red blood cell membrane. The data obtained seem to be more consistent with a counter-transport model for explaining the propranolol effect than with a mechanism based on free diffusion of K+ through the membrane.