Effect of cell volume on potassium transport in human red cells

Studies in red blood cell preservation. 7. In vivo and in vitro studies with a modified phosphate-ammonium additive solution

Studies were conducted to examine whether an experimental additive solution (EAS-2) containing, in mM: 20 NH4Cl, 30 Na2HPO4, 2 adenine, 110 dextrose, 55 mannitol, pH 7.15, would be useful to extend the storage shelf life of human RBCs. With 6 pairs of split units, ATP concentrations were better maintained for 12 weeks with EAS-2 than with Adsol (1.8 vs. 1.1 mumol/g Hb, respectively, p = 0.002). Autologous 24-hours 51Cr viability values for split units in the same donors were: on 6 paired units at 8 weeks, EAS-2 87.0 +/- 4.5%, Adsol 72.6 +/- 2.3%, p = 0.004; on 11 paired units at 9 weeks, EAS-2 79.5 +/- 7.1%, Adsol 68.2 +/- 10.1%, p = 0.0003. The data suggest that packed RBCs stored for 9 weeks with EAS-2 will be suitable for transfusion following the removal of supernatant with a single washing step.

Refrigerated storage of washed red cells

Red cells washed and stored in a citrate-phosphate-glucose-adenine solution at pH 7.4-7.6 demonstrate excellent maintenance of adenosine triphosphate, elevation of 2,3-diphosphoglycerate well above normal levels for more than 6 weeks, reduced hemolysis and 24-hour in vivo survival comparable to that of cells stored in ADSOL. These results can be attributed in part to a chloride shift in which the washout of intracellular chloride is associated with an influx of OH-, which increases intracellular pH and thereby increases the rate of glycolysis. The phosphate functions primarily as a buffer to maintain both extra- and intracellular pH. Reducing the effective osmolality of the storage solution reduces hemolysis and improves cell morphology.

Influence of loop diuretics and anions on passive potassium influx into human red cells

Passive K influx into human red cells was measured with and without Cl ions, Na ions and loop diuretics. Ouabain and loop diuretics appear to inhibit specifically and respectively the Na pump and (Na+K) 'co-transport'. Inhibitors of other pathways, e.g. 4,4'-diisothiocyantostilbene-2,2'-disulphonic acid or amiloride did not inhibit passive K influx. Loop diuretics inhibited with high apparent affinity in Na-containing media and with low apparent affinity in Na-free media where there was a substantial Cl-dependent component. The Cl concentration dependence was measured using six anion substitutions for Cl. With NO3, acetate and gluconate, the curves were sigmoidal and not fully saturable at 150 mM-Cl; with iodide and thiocyanate, the curves were convex; with sulphate, there was saturation at 120 mM-Cl. The half-maximal K influx as a function of [Na]0 was 40 mM for the Cl-dependent flux component and 12 mM for the diuretic-sensitive flux.

Role of the furosemide-sensitive Na+/K+ transport system in determining the steady-state Na+ and K+ content and volume of human erythrocytes in vitro and in vivo

To study the physiological role of the bidirectionally operating, furosemide-sensitive Na+/K+ transport system of human erythrocytes, the effect of furosemide on red cell cation and hemoglobin content was determined in cells incubated for 24 hr with ouabain in 145 mM NaCl media containing 0 to 10 mM K+ or Rb+. In pure Na+ media, furosemide accelerated cell Na+ gain and retarded cellular K+ loss. External K+ (5 mM) had an effect similar to furosemide and markedly reduced the action of the drug on cellular cation content. External Rb+ accelerated the Na+ gain like K+, but did not affect the K+ retention induced by furosemide. The data are interpreted to indicate that the furosemide-sensitive Na+/K+ transport system of human erythrocytes mediates an equimolar extrusion of Na+ and K+ in Na+ media (Na+/K+ "cotransport"), a 1:1 K+/K+ (K+/Rb+) and Na+/Na+ "exchange" progressively appearing upon increasing external K+ (Rb+) concentrations to 5 mM. The effect of furosemide (or external K+/Rb+) on cation contents was associated with a prevention of the cell shrinkage seen in pure Na+ media, or with a cell swelling, indicating that the furosemide-sensitive Na+/K+ transport system is involved in the control of cell volume of human erythrocytes. The action of furosemide on cellular volume and cation content tended to disappear at 5 mM external K+ or Rb+. The in vivo red cell K+ content was negatively correlated to the rate of furosemide-sensitive K+ (Rb+) uptake, and a positive correlation was seen between mean cellular hemoglobin content and furosemide-sensitive transport activity. The transport system possibly functions as a K+ and water-extruding mechanism under physiological conditions in vivo. The red cell Na+ content showed no correlation to the activity of the furosemide-sensitive transport system.

Volume-induced increase of K+ and Cl- permeabilities in Ehrlich ascites tumor cells. Role of internal Ca2+

Ehrlich ascites tumor cells resuspended in hypotonic medium initially swell as nearly perfect osmometers , but subsequently recover their volume within 5 to 10 min with an associated KCl loss. 1. The regulatory volume decrease was unaffected when nitrate was substituted for Cl-, and was insensitive to bumetanide and DIDS. 2. Quinine, an inhibitor of the Ca2+- activated K+ pathway, blocked the volume recovery. 3. The hypotonic response was augmented by addition of the Ca2+ ionophore A23187 in the presence of external Ca2+, and also by a sudden increase in external Ca2+. The volume response was accelerated at alkaline pH. 4. The anti-calmodulin drugs trifluoperazine, pimozide, flupentixol, and chlorpromazine blocked the volume response. 5. Depletion of intracellular Ca2+ stores inhibited the regulatory volume decrease. 6. Consistent with the low conductive Cl- permeability of the cell membrane there was no change in cell volume or Cl- content when the K+ permeability was increased with valinomycin in isotonic medium. In contrast, addition of the Ca2+ ionophore A23187 in isotonic medium promoted Cl- loss and cell shrinkage. During regulatory volume decrease valinomycin accelerated the net loss of KCl, indicating that the conductive Cl- permeability was increased in parallel with and even more than the K+ permeability. It is proposed that separate conductive K+ and Cl- channels are activated during regulatory volume decrease by release of Ca2+ from internal stores, and that the effect is mediated by calmodulin.

Study on the dehydrating effect of the red cell Na+/K+-pump in nystatin-treated cells with varying Na+ and water contents

Using the antibiotic Nystatin, we have developed a systematic method for the preparation of red blood cells with independently selected levels of intracellular Na+ concentrations and water content. Such cells provided an experimental model to study the effect of Na+/K+ pump stimulation on red cell water content. Even in initially dehydrated cells, stimulation of the Na+/K+ pump by elevated intracellular Na+ caused subsequent further loss of cell water. Cell water loss was reflected in decreased monovalent cation content per unit mass of hemoglobin and by a shift in the density distribution of the cell populations to higher densities on discontinuous Stractan gradients. We conclude that the 3 Na+out : 2 K+in stoichiometry of the Na+/K+ pump results in a net desalting effect with increased pump activity. Under the conditions of these experiments, the cell appears to have no effective mechanism to compensate for a net loss of ions and water.

Passive potassium transport in low potassium sheep red cells: dependence upon cell volume and chloride

The major pathway of passive K influx (ouabain-insensitive) was characterized in low-K type (LK) red cells of sheep. 1. Passive K transport in these cells was highly sensitive to variations in cell volume; it increased threefold or more in cells swollen osmotically by 10%, and decreased up to twofold in cells shrunken 5-10%. Active K influx was insensitive to changes in cell volume. Three different methods for varying cell volume osmotically all gave similar results. 2. The volume-sensitive pathway was specific for K in that Na influx did not vary with changes in cell volume. 3. The volume-sensitive K influx was a saturable function of external K concentration. It was slightly inhibited by Na, whereas K influx in shrunken cells was unaffected by Na. 4. Passive K influx was dependent on the major anion in the medium in that replacement of Cl with any of six other anions resulted in a reduction of K influx by 50-80% (replacement of Cl by Br caused an increase in K influx). The activation of K influx by Cl followed sigmoid kinetics. 5. Passive K influx is inhibited by anti-L antibody. The antibody affected only that portion of influx which was Cl-dependent and volume-sensitve. Of the subfractions of the antibody, it is anti-L1 which inhibits passive K transport. 6. Pretreatment of cells with iodoacetamide reduced the sensitivity of K influx to cell volume in that the influx was reduced in swollen IAA-treated cells and increased in shrunken IAA-cells. 7. Intracellular Ca has no role in altering passive K transport in LK sheep cells. Therefore, the major pathway of passive K transport in LK sheep red cells is sensitive to changes in cell volume, specific for K, dependent on Cl, and inhibited by anti-L1 antibody, The minor pathway, observed in shrunken cells, has none of these properties.

Ouabain-insensitive salt and water movements in duck red cells. III. The role of chloride in the volume response

This paper describes the effect of external chloride on the typical swelling response induced in duck red cells by hypertonicity or norepinephrine. Lowering chloride inhibits swelling and produces concomitant changes in net movements of sodium and potassium in ouabain-treated cells, which resemble the effect of lowering external sodium or potassium. Inhibition is the same whether chloride is replaced with gluconate or with an osmotic equivalent of sucrose. Since changes in external chloride also cause predictable changes in cell chloride, pH, and water, these variables were systematically investigated by varying external pH along with chloride. Lowering pH to 6.60 does not abolish the response if external chloride levels are normal, although the cells are initially swollen due to the increased acidity. Cells deliberately preswollen in hypotonic solutions with appropriate ionic composition can also respond to norepinephrine by further swelling. These results rule out initial values of cell water, chloride, and pH as significant variables affecting the response. Initial values of the chloride equilibrium potential do have marked effect on the direction and rate of net water movement. If chloride is lowered by replacement with the permeant anion, acetate, E(Cl) is unchanged and a normal response to norepinephrine, which is inhibited by furosemide, is observed. Increasing internal sodium by the nystatin technique also inhibits the response. A theory is developed which depicts that the cotransport carrier proposed in the previous paper (W.F. Schmidt and T.J. McManus. 1977b. J. Gen. Physiol. 70:81-97) moves in response to the net electrochemical potential difference driving sodium and potassium across the membrane. Predictions of this theory fit the data for both cations and anions.

Effects of Tris and histidine on human erythrocytes and conditions influencing their mode of action

1. The incubation of human erythrocytes in 0.172 M Tris - HCl, pH 7.6 buffer at 37 degrees leads to (1) a pronounced cellular volume increase, (2) a preferential release of Na+, and (3) if continued sufficiently long, hemolysis. These effects are pH dependent and also are influenced to a considerable degree by such diverse reagents as NaC glucose, and histidine. In each instance, increasing levels of the latter compounds in a Tris - HCl incubation mixture led to diminished cellular volume increase and prolonged time of onset of hemolysis. 2. Histidine solutions of 0.31 M, pH 7.5 caused a rapid and dramatic decrease in cellular volume of human erythrocytes and a concomitant rapid exit of cations. However, in a prolonged incubation, human erythrocytes slowly regained their cell volume as a result of histidine entry into the cell. Of considerable interest: Tris swollen cells undergo immediate shrinkage to far below the initial cell volume when incubated in histidine at 37 degrees C. Through repetition of this process two additional times, as much as 90-95% of the total cellular Na+ and K+ was removed without hemolysis. 3. Human erythrocytes washed in 0.12 M MgCl2 and then suspended in 0.31 M histidine, pH 7.5, lost upwards of 60% of their total Na+ and 30% of their total K+ after a 40 min incubation at 37 degrees C. However, when increasing amounts of 0.172 M Tris - HCl, pH 7.6 were added to the histidine suspension of cells, the release of K+ was reduced to 5% but the release of Na+ decreased only to 40% of the total cellular level. On the basis of these observations, it is evident that Tris exerts a preferential activity towards the efflux of Na+ from the human erythrocyte, whereas histidine results in high efflux of K+ and Na+ from the cell.

Sodium movements in high-sodium beef red cells: properties of a ouabain-insensitive exchange diffusion

1. The relative importance of the Na efflux components in beef red cells has been evaluated. The component which is insensitive to ouabain, which does not require external K but depends on the presence of external Na, accounts for about 90% of the total Na efflux.2. The experiments reported in this paper are consistent with the presence of an ouabain-insensitive Na(+)-Na(+) exchange process accounting for this ouabain-insensitive external Na dependent efflux.3. A strictly parallel behaviour of influx and efflux is observed when the pH is altered. The exchange diffusion process is inhibited over 90% by a decrease in pH from range pH 8.0-5.5.4. Both Na efflux and influx are markedly increased by raising the temperature from 27 to 37 degrees C.5. Energy depleted cells and fresh cells behave similarly in respect to Na movements. In depleted resealed ghosts, a large Na-dependent efflux occurs. No chemical energy and no special nucleotide is required for the Na(+)-Na(+) exchanges.6. When the external or internal Na concentrations are changed, a parallel behaviour of influx and efflux is observed.7. The relation between the magnitude of the exchange diffusion flux and the external or internal Na concentration fits quite well the Michaelis-Menten equation suggesting that only one Na(+) reacts with the transport mechanism. The affinity for Na is lower however at the outer surface than at the inner border of the membrane.8. The relation between this exchange process, the ouabain-insensitive Na-Na exchanges found in human red cell, and Ussing's model of exchange diffusion is discussed.

Further studies of sodium transport in feline red cells

The transport of radioactive sodium in high sodium cat red blood cells has been studied under various experimental conditions. It was found that iodoacetate (IAA) and iodoacetamide (IAM) inhibit Na influx by 50% whereas NaF has no effect. Reversible dyes, such as methylene blue (Mb), also inhibit this influx by 60%. Both IAA and Mb effects show a lag period of about 40 min. Cell starvation abolishes the volume-dependent Na influx which is generally observed in these cells. IAA reduces significantly the volume-dependent Na influx but does not inhibit it completely. 5 mM magnesium chloride produces a twofold increase in Na influx. On the other hand, MgCl(2) has no effect on Na transport in human red cells or on potassium or sulfate transport in cat red cells. The effect of MgCl(2) is quite rapid and does not interfere with the volume-dependent Na influx. This effect is abolished in starved cells. Reincubation of previously stored cells in buffered solutions containing glucose and MgCl(2) causes more than one order of magnitude increase in Na influx. These several observations are discussed in terms of the possibility of a link between Na transport and Na-Mg-activated ATPase.

Ouabain-uninhibited sodium transport in human erythrocytes. Evidence against a second pump

Others have concluded that a second Na "pump" (active Na outflux) exists in human erythrocytes. This second pump was said to be ouabain-insensitive, unlike the classic ouabain-sensitive Na-K pump. An alternative explanation is that "pump II" is Na exchange diffusion. These hypotheses were examined in the present experiments, utilizing (22)Na influx and outflux measurements, net Na fluxes, and ATPase determinations. Ouabain-uninhibited Na outflux was reduced 0.58+/-0.05 mmol/liter cells per h when extracellular Na (Na(o)) was replaced by Mg. Ethacrynic acid or furosemide produced similar decrements of outflux (0.50 mmol) in the presence of ouabain and Na(o). However, these diuretics had minimal inhibitory effects on outflux in the absence of Na(o) suggesting that they inhibited principally the Na(o)-dependent outflux. Whereas this ouabain-uninhibited portion of outflux was dependent on Na(o), it was independent of K(o). Contrary to expectations, Na influx did not change when intracellular Na was altered. No uphill, net Na transport (ouabain-uninhibited) could be demonstrated under a variety of circumstances. Furosemide at high concentrations inhibited ATPase, reducing both ouabain-sensitive and ouabain-insensitive enzyme at 1.0 mM concentration while showing no effect on ATPase at 0.05-0.1 mM concentration. The effects of furosemide on ATPase and on Na flux were dissociable on a dose-response curve. Energy depletion for 22 h practically eliminated the Na(o)-dependent, diuretic-inhibited Na outflux. Activation energies and temperature coefficients for the diuretic-inhibited outflux were one-half the values for the classic ouabain-inhibited pump. These data are interpreted as evidence against a second Na pump. Exchange diffusion accounts adequately for most of these observations; however, the ouabain-insensitive fluxes may be complex and composed of several processes.