The mechanism of vanadium action on selective K+-permeability in human erythrocytes

Reconstitution of the basal calcium transport in resealed human red blood cell ghosts

The (45)Ca(2+) influx into right-side-out resealed ghosts (RG) prepared from human red blood cells (RBC) was measured. The (45)Ca(2+) equilibration occurred with t(1/2)=2.5 min and the steady-state was reached after 17 min with the level of 22+/-2 micromol/L(packed cells) at 37 degrees C. The rate of the influx was 97+/-17 micromol/L(packed cells)h. The (45)Ca(2+) influx was saturated with [Ca(2+)](0) at 4 mmol/L and was optimal at pH 6.5 and 30 degrees C. Divalent cations (10(-4)-10(-6)mol/L), nifedipine (10(-5)-10(-4)mol/L), DIDS (up to 10(-4)mol/L), and quinidine (10(-4)-10(-3)mol/L), inhibited the (45)Ca(2+) influx while uncoupler (10(-6)-10(-5)mol/L) stimulated it. In contrast to intact RBC, vanadate inhibited the (45)Ca(2+) influx when added to the external medium, however, the stimulation was observed when vanadate was present in media during both lysis and resealing. PMA had no effect under conditions found to stimulate the Ca(2+) influx in intact RBC. The results show that the Ca(2+) influx into RG is a carrier-mediated process but without control by protein kinase C and that the influx and efflux of Ca(2+) are coupled via the H(+) homeostasis similarly as in intact RBC but with modified mechanism.

Micropipette aspiration of human erythrocytes induces echinocytes via membrane phospholipid translocation

When a discocytic erythrocyte (RBC) was partially aspirated into a 1.5-microns glass pipette with a high negative aspiration pressure (delta P = -3.9 kPa), held in the pipette for 30 s (holding time, th), and then released, it underwent a discocyte-echinocyte shape transformation. The degree of shape transformation increased with an increase in th. The echinocytes recovered spontaneously to discocytes in approximately 10 min, and there was no significant difference in recovery time at 20.9 degrees C, 29.5 degrees C, and 37.4 degrees C, respectively. At 11 degrees C the recovery time was significantly elevated to 40.1 +/- 6.7 min. At 20.9 degrees C the shape recovery time varied directly with the isotropic RBC tension induced by the pipetting. Sodium orthovanadate (vanadate, 200 microM), which inhibits the phospholipid translocase, blocks the shape recovery. Chlorpromazine (CP, 25 microM) reversed the pipette-induced echinocytic shape to discocytic in < 2 min, and the RBC became a spherostomatocyte-II after another 30 min. It was hypothesized that the increase in cytosolic pressure during the pipette aspiration induced an isotropic tension in the RBC membrane followed by a net inside-to-outside membrane lipid translocation. After a sudden release of the aspiration pressure the cytosolic pressure and the membrane tension normalized immediately, but the translocated phospholipids remained temporarily "trapped" in the outer layer, causing an area excess and hence the echinocytic shape. The phospholipid translocase activity, when not inhibited by vanadate, caused a gradual return of the translocated phospholipids to the inner layer, and the RBC shape recovered with time.

Comparison of the effects of various vanadium salts on glucose homeostasis in streptozotocin-diabetic rats

Oral administration of vanadium salts to severely diabetic rats lead to a spectacular decrease of plasma glucose levels in spite of the insulin deficiency of the animals. The insulin-like properties of vanadium have been attributed to the cationic form, vanadyl, into which the anionic form, vanadate, is reduced within cells. This has led to the suggestion that vanadyl is the form of choice for the treatment. In this study, rats made insulin-deficient and diabetic with streptozotocin were treated with three salts of vanadium: sodium orthovanadate, sodium metavanadate and vanadylsulfate. The salts were added to the drinking water, in concentrations that led to ingestion of the same amount of vanadium element by the three groups of rats (approximately 8 mg/kg per day). The initial, transient, loss of weight that affected the treated rats was slightly smaller in the vanadyl-treated group than in the vanadate-treated groups. However, during steady-state treatment, the three groups exhibited a similar food intake (lower than in controls) and growth rate (higher than in controls). The decreases in plasma glucose levels, in urinary volume and in glucosuria, and the improvement of the tolerance to an oral glucose load were similar regardless of the type of vanadium salt. Withdrawal of the treatment after 14 weeks was followed by a rapid increase in plasma glucose levels which, however, remained clearly lower than in controls for at least 4 weeks, whereas plasma insulin levels increased only transiently. A smaller glucosuria and a slightly better tolerance to oral glucose than in controls were still observed in the previously treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Vanadium induced hemolysis of vitamin E deficient erythrocytes in Hepes buffer

Several vanadium compounds were tested for their ability to induce in vitro hemolysis of vitamin E-deficient hamster erythrocytes. Free vanadyl caused hemolysis in Hepes buffer but not in Tris or phosphate buffer, while hemolysis was inhibited by catalase, chelators such as deferoxamine mesylate and EDTA, and hydroxyl radical scavengers such as ethanol and D-mannitol. Although metavanadate itself could not induce hemolysis, metavanadate with NAD(P)H caused hemolysis in Hepes buffer only, and superoxide dismutase prevented it. Hydrogen peroxide, hydroxyl radical and Hepes radical were involved in vanadyl-induced hemolysis, superoxide anion was further involved in metavanadate plus NAD(P)H-induced hemolysis. Vitamin E prevented hemolysis under both conditions.

Haematological results of vanadium intoxication in Wistar rats

1. Two-month-old rats of the Wistar strain of both sexes received, as sole drinking liquid, an aqueous solution of ammonium metavanadate (AMV) of 0.15 mg V/cm3 concentration for a period of 4 weeks. 2. A small decrease in the amount of food consumed and a significant reduction of the water AMV solution drunk were observed, as compared with the food and water taken up by the control group. 3. In the peripheral blood a significant decrease in the erythrocyte count and haemoglobin level and increased percentage of reticulocytes and polychromatophilic erythrocytes were noted. 4. No changes in the activity of lactate dehydrogenase (LDH) and glucose-6-phosphate dehydrogenase (G-6PD) were found in the erythrocytes of the animals tested. 5. The increase in the neutrophilic granulocyte and lymphocyte count was significant. 6. An inhibitory influence of vanadium on the phagocytic activity of granulocytes was observed.

Haematological effects of vanadium on living organisms

Although vanadium has been of great interest for many researchers over a number of years, its biochemical and physiological role is not yet fully clear. There are many papers describing the haematological consequences of its excess in living organisms and most of their data are quoted in this mini-review. The authors of these papers used various laboratory animals, different vanadium compounds, frequently different routes of administration and duration of intoxication. Hence a checklist and comparison of the results are rather difficult. Vanadium reduces the deformability of erythrocytes, and such cells are rather frequently retained in the reticuloendothelial system of the spleen and eliminated faster from the blood stream (Kogawa et al., 1976). Vanadium produces peroxidative changes in the erythrocyte membrane, this leading to haemolysis. Therefore, the depressed erythrocyte count in animals intoxicated with vanadium may be the consequence of both the haemolytic action of vanadium and the shortened time of survival of erythrocytes. Changes of the haem precursor level in blood serum and urine observed in humans exposed occupationally to vanadium suggest an influence of this element on haem synthesis. This problem requires, however, further studies and observations. Changes occurring under the influence of vanadium on the leukocyte system of animals suggest the influence of this element on the resistance of the organism, but the mechanism of the action of vanadium still requires elucidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of red cell Ca2(+)-activated K+ channel by Ca2+ involves a temperature-dependent step

We found that vanadate-induced 45Ca2+ uptake by red cells is maximal at 25 degrees C. At this temperature, the Cai-induced increase of the K+ permeability (the Gárdos effect) shows a lag (up to 8 min) which is not observed at 37 degrees C. This cannot be explained by the lack of availability of Ca2+ for the Ca2(+)-activated K+ channel, and suggests that its activation by Ca2+ is mediated by a temperature-dependent mechanism which remains unknown so far. The lag is not observed when the Gárdos effect was initiated by propranolol. This shows that the putative temperature-dependent step is different from chloride transport.

The effect of ferricyanide with iodoacetate in calcium-free solution on passive cation permeability in human red blood cells: comparison with the Gardos-effect and with the influence of PCMBS on passive cation permeability

Freshly prepared human red blood cells incubated with 5 mM ferricyanide, 0.2 mM iodoacetate and 2 mM adenosine in the presence of 5 mM EGTA demonstrate comparable increases in Na+ and K+ permeability (ferricyanide effect). This effect is unrelated to the Ca2+-activated K+ channel (Gardos effect) since influx of Ca2+ from outside the cell is excluded. Also this effect is different from the non-specific Na+ and K+ permeability change elicited by PCMBS. These differences become obvious by using various reagents. For example, A23187 and quinidine exert opposite effects in Gardos and ferricyanide experiments, where A23187 and atebrin react oppositely in the latter and in PCMBS experiments. The ferricyanide effect described here does not involve formation of nonspecific channels. The change in Na+ permeability separately from K+ permeability under certain circumstances suggests a more specific effect.

Modulation of the Ca2+- or Pb2+-activated K+-selective channels in human red cells. I. Effects of propranolol

To study the effect of propranolol on the Ca2+- or Pb2+-activated K+ permeability in human erythrocytes, K+ effluxes were compared with single-channel currents. The results demonstrate that propranolol has a twofold effect: (1) it renders the channel protein more sensitive to Ca2+ or Pb2+; and (2) it simultaneously inhibits channel activity and slightly reduces single-channel conductance. The number of active channels is not affected.

Polymyxin B, a novel inhibitor of red cell Ca2+-activated K+ channel

Polymyxin B (PXB), a cyclic peptide antibiotic, in concentrations 0.1-3.0 mg/ml (0.08-4.0 mmol/l), inhibited the K+ efflux induced by opening of the Ca2+-activated K+ channel (the Gárdos effect) in intact human red blood cells. The inhibition was observed when the Gárdos effect was elicited by Ca2+ in the presence of vanadate, or propranolol, in ATP-depleted cells, and in A23187-treated cells. The inhibition of the Gárdos effect is caused neither by the inhibition of the anion channel by PXB nor by the inhibition of Ca2+ entry. It can be ascribed to the inhibition of the Ca2+-activated K+ channel. The mechanism of the inhibition remains to be elucidated.

Action of di- and tri-valent cations on calcium-activated K+-efflux in rat erythrocytes

Isolated rat erythrocytes were labelled with [86Rb] as a tracer for intracellular K+. It was demonstrated that rat erythrocytes possess a Ca2+-mediated K+-efflux mechanism similar to that reported for human erythrocytes. This model was used to investigate the interactions of di- and tri-valent cations on potassium [86Rb] permeability in intact cells. Low concentrations of Ag2+ and Hg2+ haemolysed erythrocytes and Pb2+ produced a selective increase in [86Rb] efflux which became self-inhibitory at concentrations above 100 microM. The effects of Pb2+ were potentiated by A23187. Ni2+, Cu2+, Co2+, Zn2+, Fe2+, Mn2+, Y2+ and Ba2+ did not initiate [86Rb] efflux, even in the presence of 0.5 microM A23187 and at concentrations as high as 1 mM. All of these cations, except Ba2+, were potent inhibitors of [86Rb] efflux evoked by 50 microM Ca2+ + 0.5 microM A23187. The lanthanides Tb3+, Gd3+, Eu3+, Sm3+ and La3+ increased [86Rb] efflux at low concentrations in the presence of A23187, but were self inhibitory at higher concentrations. They also inhibited Ca2+-mediated [86Rb]-efflux. It is concluded that the effectiveness of a cation in activating [86Rb] efflux is, in part, related to its non-hydrated crystalline ionic radius, and that the site of activation may only accommodate ionic radii between 0.95 and 1.00 A.

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.

Lead-induced activation and inhibition of potassium-selective channels in the human red blood cell

The selective increase of net K+ permeability in human red cells brought about by either Ca2+ or lead was studied using a light scattering technique to measure net K+ fluxes in cell suspensions and the patch-clamp technique to study K+ transport in individual K+-selective channels of the red cell membrane. Using ultrapure solutions it was demonstrated that the effect of lead is neither the indirect consequence of a lead-induced increase of the accessibility of the receptor sites of the K+-selective channels to traces of Ca2+ that are present as contamination in analytical grade reagents nor to the release of Ca2+ from intracellular Ca2+ stores. It is further shown that in cell-free membrane patches low concentrations of lead (10 microM) in Suprapur solutions evoke the same single-channel events as added Ca2+ and that this activity can be inhibited by high concentrations of lead (100 microM), similar to the net KCl efflux measured by means of the light scattering technique. It is concluded, therefore, that both Ca2+ and lead independently activate the same K+-selective channels in the red cell membrane.