The effect of anti-L on ouabain binding to sheep erythrocytes

Some physiological aspects of genetic variation in the blood of sheep

The principal genetic variants in sheep red cells and plasma are listed. Current hypotheses as to how the L blood group antigen affects active potassium transport across the red cell membrane are summarized. Recent work on an inherited defect in amino acid transport which results in a red cell GSH deficiency is also described.

Characterization of fatty acid interaction with ouabain and vanadate binding to (Na+ + K+)-activated ATPase

The candidateship of unsaturated fatty acids as endogenous ouabain-like factors was studied. Binding of the artificial ligand vanadate at the intracellular phosphorylation epitope of membrane-bound Na+/K+-ATPase was unaffected by linoleic and arachidonic acid. In the (Mg2+ + Pi)-facilitated system for ouabain binding they were characterized as noncompetitive inhibitors of cardiac glycoside binding, however. The ouabain binding capacity as well as the affinity decreased and the ouabain dissociation rate was accelerated by fatty acids. In the presence of vanadate for facilitation of ouabain binding an increase in ouabain affinity was seen. It is concluded that elementary criteria for the characterization of unsaturated fatty acids as ouabain-like factors are not fulfilled. The ratio between E2-subconformations of Na+/K+-ATPase with different ouabain affinities may be changed by incorporation of fatty acids in the lipid membrane.

Na+-K+ pump activities of high- and low-potassium sheep red cells with internal magnesium and calcium altered by A23187

1. Sheep erythrocytes were treated with the divalent metal ionophore A23187 to alter the cellular magnesium (Mgi) and calcium (Cai) composition. Ouabain-sensitive Na+-K+ pump fluxes were measured using rubidium as a potassium congener in media where Cl- was replaced by NO3-. 2. A23187, per se, had no effect on ouabain-sensitive rubidium influx. However, lowering the concentration of cellular magnesium [( Mg]i) and increasing that of calcium [( Ca]i) decreased Na+-K+ pump flux. 3. Ouabain-sensitive rubidium influx was found to be a saturating function of [Mg]i in high-potassium (HK) red cells with a Hill coefficient of about 1.8 and an apparent half-activation constant (K0.5) of 0.46 mmol/(l original cells). In low-potassium (LK) cells, in the absence and presence of the Na+-K+ pump stimulatory L-antibody, ouabain-sensitive rubidium influx was also saturated with Mgi yielding Hill coefficients of close to 1.8 and K0.5 values of 0.20 and 0.30 mmol/(l original cells), respectively. 4. When [Ca]i was raised at constant [Mg]i ouabain-sensitive rubidium influx was inhibited at about 700 mumol/(l cells) in both HK, and in anti-L-treated LK red cells. 5. These data exclude the possibility that the Na+-K+ pump turnover, known to be different in HK red cells, and in LK red cells in the absence and presence of anti-L (Joiner & Lauf, 1978b), is based on differences in the activation by MgATP, and that Cai interacts with the Na+-K+ pump cycle differently in the two red cell cation types.

Cation depletion by the sodium pump in red cells with pathologic cation leaks. Sickle cells and xerocytes

The mechanism by which sickle cells and xerocytic red cells become depleted of cations in vivo has not been identified previously. Both types of cells exhibit elevated permeabilities to sodium and potassium, in the case of sickle cells, when deoxygenated. The ouabain-insensitive fluxes of sodium and potassium were equivalent, however, in both cell types under these conditions. When incubated 18 hours in vitro, sickle cells lost cations but only when deoxygenated. This cation depletion was blocked by ouabain, removal of external potassium, or pretreatment with 4,4'-diisothiocyanostilbene-2,2'-disulfonate, which blocks the increase in cation permeability induced by deoxygenation. The loss of cation exhibited by oxygenated xerocytes similarly incubated was also blocked by ouabain. These data support the hypothesis that the elevated "passive" cation fluxes of xerocytes and deoxygenated sickle cells are not directly responsible for cation depletion of these cells; rather, these pathologic leaks interact with the sodium pump to produce a net loss of cellular cation.

Effects of insulin on the total number of [3H]ouabain binding sites in normal human lymphocytes and after stimulation in vitro with concanavalin A

The effects of insulin in vitro on the total number of [3H]ouabain binding sites were studied in normal and concanavalin A-stimulated human T-lymphocytes after incubation for 18 and 42 h with 0, 10(2) and 10(5) mIU/l of insulin. While no effect on [3H]ouabain binding could be demonstrated in non-stimulated cells, a significant decrease could be produced in concanavalin A-stimulated cells. Mean +/- SD for the total number of [3H]ouabain binding sites per cell after 18 h incubation time with concanavalin A in the absence of insulin was 46,099 +/- 6,620 as compared with 44,783 +/- 8,347 in the presence of 10(2) mIU/l of insulin (non-significant) and 42,406 +/- 7,066 in the presence of 10(5) mIU/l (p = 0.031). The corresponding 42-h values were 47,075 +/- 9,412, 43,761 +/- 9,273 (p = 0.033) and 43,824 +/- 9,312 (p = 0.005).

Solubilization and further chromatographic purification of highly purified, membrane-bound Na,K-ATPase

Highly purified membrane-bound Na,K-ATPase from pig kidney outer medulla was dissolved in the non-ionic detergent C12E8. Chromatography of the dissolved material on a DEAE matrix yielded enzymatical material having a ouabain-binding capacity of 6.9 nmoles per mg protein (measured according to Lowry et al., with bovine serum albumin as standard). This material, which after addition of lipids had the same K+-phosphatase turnover as the membrane-bound enzyme, could consist entirely of live molecules with a molecular weight of 145 kDa, a value close to that expected for alpha beta-promoters of Na,K-ATPase.

Mechanism of alteration of sodium potassium pump of erythrocytes from patients with chronic renal failure

We examined intracellular electrolytes, K influx, and [3H]ouabain-binding capacity of erythrocytes from 32 normal subjects and 45 patients with end-stage renal failure on dialysis, including 16 with high intracellular Na (mean 17.3 +/- 3.9 mmol/liter cell water). The [3H]ouabain-binding capacity of erythrocytes with high cell Na was markedly reduced as compared with that of erythrocytes from normal subjects (274 +/- 52 vs. 455 +/- 59 sites/cell, P less than 0.001). The mean serum creatinine was higher in the uremic group with high cell Na. There was a significant linear correlation between intracellular Na and [3H]ouabain-binding in both normal and uremic subjects. Cross-incubation of normal cells with uremic plasma for 24 h failed to reduce [3H]ouabain-binding capacity of normal cells. In spite of a substantial increase in cell Na, K pump influx was not higher in uremic erythrocytes with high cell Na. When intracellular Na was altered with nystatin (cell Na equal to 120 mmol/liter cell water in both groups), K pump influx was proportional to the number of Na-K pump sites so that the ion turnover rate per pump site was similar in the two groups. Uremic plasma failed to depress K pump influx of normal erythrocytes. The passive net influx of Na in uremic cells with high intracellular Na was not different from that observed in erythrocytes from normal subjects. When erythrocytes were separated by age on Percoll density gradients, the number of Na-K pump sites of the youngest uremic cells was significantly lower than that of the youngest normal cells, suggesting that decreased synthesis of Na-K pump sites, rather than accelerated loss of Na-K pump sites during aging, was responsible for the decrease in [3H]ouabain-binding capacity of erythrocytes from uremic subjects. Taken together, these findings suggest that a decrease in the number of Na-K pump sites plays a major role in the abnormality of Na-K pump of erythrocytes from patients with chronic renal failure.

Inverse relationship between ouabain sites on human erythrocytes and body mass index in normal healthy subjects

Binding of [3H]ouabain by erythrocytes and levels of (Na+ + K+) ATPase, cell sodium and potassium, and plasma triiodothyronine (T3) were studied in 16 normal, apparently healthy men. The subjects were between 28 and 50 years of age. Based on their economic status, the subjects were divided into two groups of eight each. Group A consisted of subjects with a higher economic status; these subjects had a mean body mass index (weight/height2) of 24.1 +/- 1.2 (mean +/- SEM). Group B comprised subjects with a lower economic status; these subjects had a mean body mass index of 18.8 +/- 1.0. The number of ouabain binding sites per red cell in group B was higher (466 +/- 29) compared with that in group A (348 +/- 21; P less than 0.01). The dissociation constant (Kd) between the two groups was not different. The (Na+ + K+) ATPase activity per 10(10) cells in group B (0.50 +/- 0.07) was higher compared with that in group A (0.29 +/- 0.03). The increased number of pump sites and increased enzyme activity in group B were associated with a lower [Na]-to-[K] ratio in the cell (P less than 0.01). The plasma T3 level in group A (202 +/- 16.7 ng/dL) was not statistically different from that of group B (163 +/- 17.6 ng/dL). The number of sodium pump sites showed an inverse relationship with body mass index (r = -0.55; P less than 0.05) and with the cell [Na]-to-[K] ratio (r = -0.74; P less than 0.01). The number of pump sites in group A showed a positive correlation (r = 0.60) with plasma T3 levels. Such a relationship was, however, weak in group B (r = 0.36). The results lead to the conclusion that there was increased utilization of available cell energy by sodium pump activity in the subjects in group B. This may be a physiologic adaptation for efficient utilization of ingested nutrients via the sodium pump in response to marginal nutrient deficits in these subjects. Dissociation of increased pump sites from plasma T3 levels may mean that the adaptive phenomenon does not represent a wasteful loss of energy.

The response to potassium of the Na-K pump ATPase in low-K red blood cells from cattle at birth and in later life

It is shown that in low-K red blood cells of cattle the apparent affinity for K(1/Kapp K) at an inhibitory site of the Na-K ATPase increases markedly during the first 3 months of life. This site probably is the Na accepting site at the internal membrane surface and the change in Kapp K reflects an increase in KNa/KK, the ratio of the true dissociation constants. This effect may explain the concomitant fall in cellular K concentration.

[3H]Ouabain binding and Na+, K+-ATPase in resealed human red cell ghosts

The interaction of the cardiac glycoside [3H]ouabain with the Na+, K+ pump of resealed human erythrocyte ghosts was investigated. Binding of [3H]ouabain to high intracellular Na+ ghosts was studied in high extracellular Na+ media, a condition determined to produce maximal ouabain binding rates. Simultaneous examination of both the number of ouabain molecules bound per ghost and the corresponding inhibition of the Na+, K+-ATPase revealed that one molecule of [3H]ouabain inhibited one Na+, K+-ATPase complex. Intracellular magnesium or magnesium plus inorganic phosphate produced the lowest ouabain binding rate. Support of ouabain binding by adenosine diphosphate (ADP) was negligible, provided synthesis of adenosine triphosphate (ATP) through the residual adenylate kinase activity was prevented by the adenylate kinase inhibitor Ap5A. Uridine 5'-triphosphate (UTP) alone did not support ouabain binding after inhibition of the endogenous nucleoside diphosphokinase by trypan blue and depletion of residual ATP by the incorporation of hexokinase and glucose. ATP acting solely at the high-affinity binding site of the Na+, K+ pump (Km approximately 1 microM) promoted maximal [3H]ouabain binding rates. Failure of 5'-adenylyl-beta-gamma-imidophosphate (AMP-PNP) to stimulate significantly the rate of ouabain binding suggests that phosphorylation of the pump was required to expose the ouabain receptor.

The effect of harmaline on unidirectional potassium fluxes and ouabain binding in renal cell cultures

Harmaline inhibits K+ influx into primary cell cultures of ground squirrel kidneys to a greater extent than either ouabain or furosemide. A concentration of 200 microM harmaline was required to inhibit half of the total K+ influx; this effect was also seen at low temperature (5 degrees C), and in another species (hamster). Although kinetic analysis of K+ influx indicates that harmaline does not compete with extracellular K+, harmaline did reduce the binding of [3H]ouabain to the cells. K+ efflux was also reduced. Therefore, harmaline may inhibit the furosemide-sensitive Na+/K+ cotransport system as well as the ouabain-sensitive Na+/K+ pump.

The K+-induced apparent heterogeneity of high-affinity nucleotide-binding sites in (Na+ + K+)-ATPase can only be due to the oligomeric structure of the enzyme

K+ induces an apparent heterogeneity among an otherwise homogeneous population of nucleotide-binding sites in (Na+ + K+)-ATPase preparations from pig kidney. With the help of ouabain we show that this heterogeneity cannot be due to a mixture of different and independent sites and conclude that each enzyme molecule must contain two nucleotide site-containing units that show interaction. Na+ induces an apparent heterogeneity among an otherwise homogeneous population of ouabain-binding sites. The argument is, therefore, extended to include one ouabain site on each of the structural units that bind nucleotide. All these structural units are shown to hydrolyse substrate at identical rates. Using the presently available molecular weight data, it is concluded that the enzyme is composed of two subunits each possessing one nucleotide-binding site, one ouabain-binding site, one alpha-peptide and the capacity for hydrolysing ATP and p-nitrophenyl phosphate.

[3H]Ouabain binding to human erythrocytes in protein-énergy malnutrition

[3H]Ouabain binding to erythrocytes was determined in normal children and in children suffering from kwashiorkor or marasmus. Scatchard plot analysis of [3H]ouabain binding displayed straight lines with linear slopes in all subjects indicating the presence of a single species of ouabain binding sites on erythrocytes. The number of ouabain binding sites per cell was 385 +/- 26 (mean +/- SEM, n = 3) in normal, 891 +/- 102 (n = 8) (p less than 0.001) in kwashiorkor and 316 +/- 45 (n = 3) in marasmic children. The equilibrium dissociation constant (Kd) for ouabain binding in kwashiorkor (16 nmol/1) was similar to that in control (12 nmol/1). The specific activity of Na+, K+ -ATPase of erythrocyte membrane has been shown to be higher in kwashiorkor children as compared to normal children [3]. This increase in enzyme activity may be considered as a consequence of increase in the enzyme content as indicated by the increased number of ouabain binding sites on red cells. Elevation in the level and activity of erythrocyte Na+, K+ -ATPase in kwashiorkor might represent a compensatory mechanism in response to a primary membrane abnormality, to effect prevention of Na+ accumulation and K+ depletion inside the cell.

Glucocorticoid-induced alterations in the sodium potassium pump of the human erythrocyte

To evaluate the effects of glucocorticoids on the Na-K pump in human subjects, were evaluated the intracellular sodium and potassium, 42K influx across and the [3H]ouabain binding to cell membranes of intact human erythrocytes from a group of subjects taking glucocorticoids and a group of normal subjects. Intracellular sodium concentration was lower (7.2 +/- 0.4 vs. 10.9 +/- 0.2 mmol/liter cell water) and intracellular potassium concentration higher (149.8 +/- 1.5 vs. 137.2 +/- 1.2 mmol/liter cell water) in erythrocytes from steroid-treated patients. In spite of a significantly decrease intracellular sodium which normally diminishes ouabain-sensitive 42K influx, the ouabain-sensitive K influx was unchanged in erythrocytes from the steroid-treated group. Maximum [3H]ouabain binding was markedly higher in the steroid-treated group (835 +/- 44 vs. 449 +/- 11 sites/cell). There was close linear correlation between [3H]ouabain binding and inhibition of K pump, suggesting the specificity of ouabain binding to Na-K pump sites on the cell membrane. Association kinetics for ouabain were similar in the two groups despite the marked difference in the amount of [3H]ouabain binding. External potassium concentration required for half-maximum ouabain-sensitive K influx was identical in the two groups. Thus, the additional Na-K pump sites in the steroid-treated group were qualitatively similar to those in normals. These results suggest that administration of glucocorticoids leads to an increase in the number of Na-K pump sites. The increase in the number of Na-K pump sites may explain the low levels of intracellular sodium and higher cell potassium observed in steroid-treated subjects.

Increased human red cell cation passive permeability below 12 degrees C

The rate of most biological reactions declines as the temperature is reduced; indeed, cooling is often used to limit or terminate reactions. We report here a paradoxical temperature response of red cell K and Na permeability below 12 degrees C. This may be interpreted thermodynamically in terms of a membrane-ordering phenomenon, an observation supported by a variety of other physical measurements on red cell membranes reported in the literature.

Effect of concanavaline A on intracellular K+ and Na+ concentration and K+ transport of human lymphocytes

Incubation of human lymphocytes with ConA causes an increase in [Na+]i and a decrease in [K+]i. This effect is not due to the experimental washing procedure, but is due to the ConA-induced increase in permeability which is not fully compensated by the increase in active transport. The ConA-induced increase in 42K+ uptake consists of an increase in leak flux which is independent of [Na+]o, and of an increase in pump flux which is dependent on [Na+]o. The increase in leak flux may be caused by increased membrane fluidity. The increase in pump flux may be produced by the increased [Na+]i and by a stimulation of Na+, K+ATPase.

LK sheep reticulocytosis: effect of anti-L on K influx and in vitro maturation

After massive hemorrhage, adult sheep with genotypically low potassium (LK) red cells temporarily produce high potassium (HK) cells with ouabain-sensitive K+ pump fluxes equivalent to mature HK red cells. In light of recent reports of different red cell volume populations accompanying the HK-LK transition also occurring in newborn LK sheep and the unresolved controversy over the effect of anti-L on K+ transport in these immature red cells, we have reexamined the K+ transport changes and the effect of anti-L in the newly formed HK cells at various times after anemic stress and under in vitro conditions. We found that approximately 7 d after bleeding, maximum reticulocytosis occurred in the peripheral blood. After separation by density centrifugation, the top 10% cell fraction contained 100% reticulocytes, with a mean cell volume 2.5 times larger than that of mature erythrocytes. These immature red cells were of HK type, and their K+ pump and leak fluxes were 30 and 10 times higher, respectively, than those found in mature LK cells. The new cells may possess HK- and LK-type pumps because K+ pump influx was significantly stimulated by anti-L. When separated by density centrifugation on days 9, 17, and 23 after bleeding, some of the cells apparently maintained their large size while gaining higher density. Large cells from day 9, kept in vitro for 22 h, showed anti-L-sensitive K+ pump and leak fluxes that declined within hours, paralleling the behavior of these cells in vivo, whereas cellular K+ levels changed much less. It is concluded that the newly formed red cells may belong to a stress-induced macrocytic cell population that does not acquire all of the characteristics of adult LK cells.

Stimulation of the sodium-potassium pump by trypsin in low potassium type erythrocytes of goats

1. Treatment of low K goat red cells with trypsin stimulated the Na-K pump more than twofold. Dose dependence and time course experiments indicated a half-maximal stimulation at 1.6 mg trypsin/ml. (37 degrees C, 3 hr), and a maximum effect after 5 hr (10 mg/ml). 2. Trypsin had only a small and variable effect on the ouabain-insensitive component of K influx. 3. The Na-K pump activity of high K goat red cells was not affected by trypsinization. 4. When intracellular K was varied by the PCMBS technique, it was found that the trypsin stimulation was greatest (2-5-fold) in cells with the highest K (40 m-mole/1. cells) and lowest (1.1-fold) in cells with low K (<1 m-mole/1. cells). 5. The trypsin effect was reversed by nystatin treatment or hypotonic lysis. 6. Trypsin did not increase the number of ouabain-binding sites. 7. It is concluded that trypsinization modifies the L antigen in low K goat red cells to decrease the apparent internal affinity for K of the Na-K pump in these cells.

Membrane cholesterol depletion and K+ transport in high and low potassium sheep red cells

The effect of cholesterol depletion on potassium tracer fluxes was studied in sheep red cells. Removal by the plasma incubation method (5, 12, 30) of approximately 31 and 34% membrane cholesterol from high-potassium (HK) and low-potassium (LK) sheep red cells, respectively, did not induce significant changes in the steady-state cation composition of these cells nor in their passive (leak) and active (pump) K+ influxes. In cholesterol-depleted LK sheep red cells, there was no impairment nor augmentation of the Lp an antibody stimulated K+ pump flux and L1-antibody-mediated reduction of K+ leak flux indicating that the removed cholesterol does not contribute to the activity of the Lp and L1 antigens.

Temperature dependence of active K+ transport in cation dimorphic sheep erythrocytes

Arrhenius diagrams of K+ pump fluxes measured between 15 degrees C and 41 degrees C were discontinuous in high K+ but not in low K+ sheep red cells. Exposure of low K+ cells to anti-L caused a bimodal temperature response of K+ pump flux with a transition temperature, Tc, similar to that found in high K+ cells but with comparatively higher activation energies above Tc.

The correlation between ouabain binding and potassium pump inhibition in human and sheep erythrocytes

1. [3H]Ouabain binding to human and sheep red blood cells was shown to be specific for receptors associated with Na/K transport. Virtually all tritium binding was abolished by dilution with unlabelled drug. Saturation levels of binding were independent of glycoside concentration and were identical to those associated with 100% inhibition of K pumping. 2. [3H]Ouabain binding and 42K influx were measured simultaneously in order to correlate the degree of K pump inhibition with the amount of glycoside bound. Results by this method agreed exactly with those obtained by pre-exposing cells to drug, followed by washing and then measuring K influx. 3. Plots of [3H]oubain binding vs. K pump inhibition were rectilinear for human and low K (LK) sheep red cells, indicating one glycoside receptor per K pump site and functional homogeneity of pump sites. High K (HK) sheep red cells exhibited curved plots of binding versus inhibition, which were best explained in terms of one receptor per pump, but a heterogeneous population of pump sites. 4. External K reduced the rate of glycoside binding, but did not alter the relationship between binding and inhibition. 5. The number of K pump sites was estimated as 450--500 per human cell and 30--50 per LK sheep cell. HK sheep cells had 90--130 sites per cell, of which eighty to ninety were functionally dominant. The number of K pump sites on LK sheep cells was not changed by anti-L, although the maximum velocity of pump turnover was increased.

Modulation of ouabain binding and potassium pump fluxes by cellular sodium and potassium in human and sheep erythrocytes

1. Erythrocytes were treated with nystatin to alter internal Na (Nai) and K (Ki) composition. Although the rates of K pumping and [3H]ouabain binding were altered dramatically, the relationship between glycoside binding and K pump inhibition was unaffected. 2. Human cells with high Nai and low Ki exhibited an increased rate of ouabain binding as compared to high Ki, low Nai cells; this paralleled the stimulated K pump activity of high Nai cells. 3. At constant Ki, increasing internal Na stimulated K pump and ouabain binding rates concomitantly. 4. At low Nai, increasing Ki inhibited both K pumping and ouabain binding. However, at high Nai, increasing Ki from 4 to 44 mM stimulated the rate of glycoside binding, parallel to its effect of increasing the rate of active K influx. 5. Anti-L, an isoantibody to low K (LK) sheep red cells, increased the rate of ouabain binding via its stimulation of K pump turnover. Since the latter effect is the result of affinity changes at the internal cation activation site(s) of the pump (Lauf, Rasmusen, Hoffman, Dunham, Cook, Parmelee & Tosteson, 1970), the antibody's effect on ouabain binding reflected the positive correlation between the rates of K pump turnover and glycoside binding. 6. These data provide the first evidence in intact cells for the occurrence of a Nai-induced conformational change in the Na/K pump during its normal operational cycle.

Irreversible inhibition of sodium entry sites in frog skin by a photosensitive amiloride analog

A photosensitive binding reaction is described in which an analog of amiloride is bound to sites that control sodium entry into frog skin. This reaction results in irreversible inhibition of net sodium transport.

Ouabain binding and potassium transport in young and old populations of human red cells

Human red blood cells were separated according to density by centrifugation through mixtures of phthalate esters. The densest 20% of the erythrocyte population (old cells) had reduced volume and water content compared to the lightest 20% of the cells (young cells). Corpuscular hemoglobin content was unchanged. Young cells had 50% more potassium (K+) than old cells, but their total intracellular concentration was only slightly higher, old cells had a small increase in sodium (Na+) concentration. Active K+ transport of young cells was 37% higher than that of old cells. [3H] + Ouabain binding revealed that this difference was the result of more K+ pump sites on young cells, which bound 530 ouabain molecules per cell at 100% K+ pump inhibition, as compared to 400 for old cells; unseparated cells bound 450-500 molecules. The relative rates of ouabain binding were identical for the two cell types. Old cells exhibited a greater passive permeability to K+, having a rate coefficient for ouabain-insensitive K+ influx 1.8 times that of young cells. There is evidence to suggest that in the face of reduced pump activity this augmented K+ "leak" might enhance the osmotic stability of the old cells and function to lengthen their life span.

Active Na-K transport and the rate of ouabain binding. The effect of insulin and other stimuli on skeletal muscle and adipocytes

1. The effect of stimulation or inhibition of active Na-K transport on [(3)H]ouabain binding has been investigated in isolated soleus muscles and adipocytes.2. In rat soleus muscle, the ouabain-sensitive component of (42)K influx was stimulated by insulin (100 m-u/ml.), adrenaline (6 x 10(-6)M), and by pre-incubation with veratrine (10(-5)M) or in a K-free buffer. In all of these instances, the rate of ouabain binding was increased by 41-113%. Conversely, pre-treatment with tetracaine (0.2 mM) decreased the (42)K-influx and diminished the rate of [(3)H]ouabain binding by 36%.3. Neither insulin, adrenaline or tetracaine produced any detectable change in the total number of ouabain-binding sites (as measured under equilibrium conditions) in rat soleus muscle.4. In mouse and guinea-pig soleus muscle and in fat cells isolated from rats, insulin also increased the rate of [(3)H]ouabain binding without producing any significant change in the total number of ouabain-binding sites.5. Both in soleus muscle and the epididymal fat pad of the rat, there was a linear correlation between (42)K influx and the initial rate of [(3)H]ouabain binding.6. It is concluded that the rate of ouabain binding is determined significantly by the rate of active Na-K transport, but within the time intervals studied (4-6 hr) stimulation or inhibition of the Na pump does not lead to any appreciable change in the total number of Na pumps. It seems unlikely that the stimulation of active Na-K transport by insulin or adrenaline is due to unmasking or de novo synthesis of Na pumps.

Active potassium transport in reticulocytes of high-K+ and low-K+ sheep

The kinetics of active K+ transport were studied in immature red blood cells cells from high-K+ and low-K+ sheep particulary with respect to the effects of varying intracellular K+ concentration, [K]i. Comparison was made with active transport, or pump, activity in mature high-K+ and low-K+ red cells. Reticulocytes from both types of sheep had much higher maximal active K+ influxes than did mature cells. In both types of reticulocytes, and in mature high-K+ cells as well, the pump was relatively insensitive to increasing [K]i. In contrast, intracellular K+ markedly inhibited the pump in mature low-K+ cells. Active K+ transport in low-K+ reticulocytes, however, as in mature low-K+ cells, is stimulated by specific isoimmune anti-L serum. Therefore the K+ pumps of high-K+ and low-K+ reticulocytes have similar kinetic properties. Maturation of the red cells, involving inactivation of most of the pump activity in both cell types, results in mature high-K+ and low-K+ cells with K+ pumps of very different kinetic characteristics.

The number and specificity of L antigen sites on low potassium type sheep red cells

Pig anti-sheep IgG conjugated, to haemocyanin was used as a marker to visualize by electron microscopy the L and. M antigen sites on sheep red cells. The number of sites seen correlated well with the results of serological and potassium transport studies and supported the concept that there are qualitative as well as quantitative differences in the expression of L antigen on the membrane of LK type cells. A tentative estimate of 340 L p sites on homozygous LK and 120 on heterozygous LK cells was made.

Binding characteristics of M and L isoantibodies to high and low potassium sheep red cells

Binding of highly purified 125I labeled M and L antibodies, both belonging to the immunoglobulin G class, was studied in high potassium (HK) and low potassium (LK) sheep red cells. Anti-M and anti-L bound specifically to M and L antigen positive HK and LK red cells, respectively. Nonspecific binding was higher for anti-L to HK cells than for anti-M to LK cells. Once bound, the M and L antibodies were capable of inducing complement dependent immune hemolysis. Only 75-100 and 500-750 molecules of anti-M and anti-L immunoglobulins were required to hemolyze 50% of HK (MM) and LK (LL) red cells, respectively, suggesting that the M and L antigens may be clustered on the surfaces of these cells. Equilibrium binding studies revealed that the maximum number of M sites is 3-6 x 10(3) in HK (MM) and 1.5-4 x 10(3) in LK (LM) cells, respectively. In comparison, the number of L antigens is slightly lower in LK cells, about 1.2-1.8 x 10(3) in LL and less in LM(LK) red cells. The number of M and L antigens, therefore, is more than an order of magnitude larger than that of the Na+K+ pumps measured previously in these cells by 3H-ouabain binding, thus precluding a quantitative correlation between M and L antigens and the Na+K+ pumps different in the three genetic types of sheep red cells. The binding affinities of both anti-M and anti-L could not be described by a single equilibrium dissociation constant indicating heterogeneous antibody populations and /or variability in the antigenic sets of individual HK or LK cells. The pronounced heterogeneity of antigens and/or antibodies in both the M and L systems was reflected in the antibody association kinetics, which also exhibited a remarkable temperature dependence. The data suggest that the correlation between the M and L antigens and the Na+K+ pump molecules is more complex than that in goat red cells previously reported by others.