Erythrocyte ghost Na+,K+-ATPase and blood pressure

To examine the relationship between body mass index, blood pressure, and the Na+,K+-adenosine triphosphatase (ATPase) system, we measured the erythrocyte ghost Na+,K+-ATPase and the erythrocyte Na+ concentration in 120 blacks and 127 whites (136 males and 111 females). Blacks showed a 13.9% higher erythrocyte Na+ (7.63 +/- 0.19 vs 6.70 +/- 0.11 [SEM] mEq/L; p = 0.0001) and a 16.1% lower erythrocyte ghost Na+,K+-ATPase activity (140.3 +/- 4.2 vs 167.3 +/- 4.7 nmol inorganic phosphate/mg protein/hr; p = 0.0002) than whites. Male subjects demonstrated a 6.4% higher erythrocyte Na+ (7.35 +/- 0.17 vs 6.91 +/- 0.14 mEq/L; p = 0.043) and an 11.5% lower Na+,K+-ATPase activity (145.7 +/- 3.7 vs 164.7 +/- 5.5 nmol inorganic phosphate/mg protein/hr; p = 0.0015) than female subjects. Significant (p less than 0.001) negative correlations were identified for the systolic, diastolic, and mean blood pressure levels and the erythrocyte ghost Na+,K+-ATPase. These findings were complemented by positive correlations for the blood pressure levels and erythrocyte Na+ concentrations. The body mass index was negatively correlated with erythrocyte ghost Na+,K+-ATPase and it accounted for 6.7%, 5.6%, and 6.1% of the variabilities in the systolic, diastolic, and mean blood pressure levels, respectively. Variabilities of 1.4% systolic, 12.3% diastolic, and 11.1% in mean arterial pressure were attributable to the erythrocyte ghost Na+,K+-ATPase activity. Provided that findings in erythrocytes also reflect the relative status of the vascular smooth muscle cell Na+,K+-ATPase, the predisposition of black, male, and obese persons to hypertension may relate, among other factors, to a lower activity of this enzyme system, which results in an increased vascular tone.     

Chronic dietary sodium overload and release of a circulating Na+-K+ pump inhibitor

High Na+ intake has been proposed to induce a rise in the activity of a circulating inhibitor of the Na+, K+-pump. The effects on male Wistar rats of a high sodium diet (8 per cent NaCl) on the activity of such a plasma Na+, K+-ATPase inhibitor were investigated. Systolic blood pressure, body weight, urinary Na+ excretion, haematocrit, intraerythrocytic Na+ content and the activity of a Na+ dependent transport system, i.e. the uptake of 5-HT by blood platelets were measured in parallel. After one week, neither systolic blood pressure nor intraerythrocytic Na+ content were modified, but the ability of the plasma extracts to inhibit renal Na+, K+-ATPase increased (70.9 +/- 1.7 vs 76.3 +/- 2.1 mumol Pi/mg/h; p = 0.05). After two weeks, the plasma inhibitory activity, the systolic blood pressure and the intraerythrocytic Na+ content were higher than that of control animals (65.5 +/- 1.6 vs 79.1 +/- 2.8 mumol Pi/mg/h, p less than 0.001; 132 +/- 2 vs 114 +/- 4 mmHg, p. +/- 0.001 and 4.95 +/- 0.32 vs 3.81 +/- 0.36 mmol/l.cells, p less than 0.05). After three months, the ability of plasma extracts to inhibit the Na+ pump and the systolic blood pressure were still elevated (57.8 +/- 1.8 vs 72.9 +/- 1.8 mumol Pi/mg/h, p less than 0.001; 145 +/- 4 vs 118 +/- 2 mmHg, p less than 0.001) whereas intraerythrocytic Na+ content had returned to control levels and 5-HT uptake was not modified.(ABSTRACT TRUNCATED AT 250 WORDS)     

Myocardial Na+,K(+)-ATPase in tachycardia induced cardiomyopathy.

Na+,K(+)-ATPase is a major determinant of myocyte homeostasis and excitation-contraction. Cardiac glycosides such as digitalis and ouabain increase the inotropic state of the heart through the inhibition of Na+,K(+)-ATPase. While cardiac glycosides are commonly used in the setting of congestive heart failure, optimal therapy would depend upon an intact Na+,K(+)-ATPase system. Changes in Na+,K(+)-ATPase activity and glycoside receptor density with the development of cardiomyopathy have not been well defined. Accordingly, left ventricular (LV) function and Na+,K(+)-ATPase activity and glycoside binding were examined in 7 pigs with dilated cardiomyopathy and in 7 controls. Dilated cardiomyopathy was produced by pacing induced supraventricular tachycardia (SVT) for 3 weeks at 240 bpm. Left ventricular function was examined by simultaneous echocardiography and catheterization. Left ventricular fractional shortening significantly decreased with SVT (34 +/- 2 vs. 10 +/- 2%, P less than 0.05) and LV diastolic dimension and pressure significantly increased (3.8 +/- 0.3 vs. 5.1 +/- 0.4 cm, and 8 +/- 2 vs. 27 +/- 2 mmHg, respectively, P less than 0.05) as compared to controls. Na+,K(+)-ATPase activity was assayed as potassium dependent p-nitrophenol-phosphatase activity. Glycoside receptor density (Bmax) and affinity (KD) was determined using [3H]-ouabain binding assays. Na+,K(+)-ATPase activity, Bmax, and KD all significantly fell from control values with SVT induced cardiomyopathy (0.64 +/- 0.06 vs. 0.45 +/- 0.12 micrograms pNP/mg/h, 5.5 +/- 0.4 vs. 1.9 +/- 0.4 pmol/mg, and 15 +/- 3 vs. 9 +/- 3 nM, respectively, P less than 0.05). The distribution of Na+,K(+)-ATPase in LV sections taken from control and SVT hearts were examined using immunohistochemical techniques. A patchy distribution of Na+,K(+)-ATPase along the sarcolemma in SVT sections was observed as opposed to a more uniform distribution in control myocytes. There was no observable change in the relative content and distribution of the Na+,K(+)-ATPase isoforms alpha 2 and alpha 3 in the SVT sections as compared to controls. In an additional set of experiments, changes in LV as well as isolated myocyte responsiveness to ouabain were examined. Left ventricular fractional shortening and peak dP/dt were measured following administration of 20-60 micrograms/Kg of ouabain in control (n = 3) and SVT (n = 3) pigs. In the control group, 40 micrograms/Kg caused a 25% in LV fractional shortening and a 60% increase in peak dP/dt from baseline. Cumulative doses of 60 micrograms/Kg in the control pigs resulted in over a 75% increase in peak dP/dt from baseline values.(ABSTRACT TRUNCATED AT 400 WORDS)     

Erythrocyte thermogenesis in hyperthyroid patients: microcalorimetric investigation of sodium/potassium pump and cell metabolism

Erythrocyte thermogenesis was studied by microcalorimetry in 11 patients before and after treatment for hyperthyroidism. Cell heat production rate and intracellular Na+ and K+ levels were measured in plasma suspensions of erythrocytes with and without specific inhibition of Na/K ATPase by ouabain. The ouabain induced change in the heat production rate (the Na/K pump thermal power); the erythrocyte intracellular Na+ content and the ouabain sensitive Na+ transport were used to estimate the Na/K pump function. The mean value for heat production rate was 131 +/- 4 mW/L erythrocytes before treatment, which is significantly higher than in euthyroid subjects. A significant decrease (P less than 0.01) to normal levels was recorded following therapy. This decrease, as determined in samples with ouabain, correlated to changes in serum levels of triiodothyronine, T3, (r = .74, P less than 0.01). The Na/K pump thermal power was 11 +/- 2 mW/L erythrocytes (8 +/- 2% of total heat production rate) before and 9 +/- 2 mW/L erythrocytes (8 +/- 2%) after treatment. These two values were not different from those obtained in euthyroid subjects. The erythrocyte Na+ content decreased from 9.9 +/- 2.1 to 4.9 +/- 0.5 mmol/L erythrocytes (P less than 0.001) following normalization of thyroid function. The decrease in intracellular Na+ concentration correlated to the decrease in serum T3 levels, but only when calculated from the data obtained in samples with ouabain (r = .60, P less than 0.05). The relative increase in intracellular Na+ concentrations following addition of ouabain was significantly lower (P less than 0.05) before than after treatment for hyperthyroidism, 37 +/- 10% and 61 +/- 5%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of sodium and potassium pump activity and number in diabetic erythrocytes

The Na+,K+-ATPase (= Na pump), which produces the concentration gradient of Na+ and K+ across the cell membrane, was studied in diabetic erythrocytes. The activity and number of Na pumps, which are functional and quantitative expression of the Na+,K+-ATPase in erythrocytes, were measured by ouabain-sensitive 42K or 43K influx and by [3H]ouabain binding, respectively. The turnover rate of the pumps was calculated from the two measurements to evaluate in situ activity of the pump. The Na pump activity was found to be higher in the diabetic (193 +/- 12 nmol K+/h . 10(9) cells) than in the normal group (164 +/- 6) (P less than 0.05), though the affinities of the pump for extracellular K+ were not different. The number of Na pumps and the Kd of the pumps for ouabain in the diabetic group were not significantly different from those in the normal group (354 +/- 12 site/cell and 4.33 +/- 0.20 nM). The turnover rate of the diabetic group tended to be higher than that of the normal group. The rate was about one third of the molecular activity reported for Na+,K+-ATPase under optimum conditions. These results indicate that the enzymatic properties as well as the number of Na pumps were not altered in diabetic erythrocytes despite the increased Na pump activity. Therefore the increased activity of the erythrocyte Na pump in diabetes mellitus suggests an increase of cation permeability associated with a possible disorder in the diabetic membrane.     

Recovery of erythrocyte Na(+)-K(+)-Cl- cotransport activity by enalapril

We studied total exchangeable sodium, ion transport activity at maximal rate, and erythrocyte Na+ content in response to angiotensin converting enzyme inhibition in mild-to-moderate essential hypertensive patients with normal renal function. Twenty-five patients (mean age 56 years, range 40-62 years) who had abnormal red blood cell Na(+)-K(+)-Cl- cotransport or red blood cell Li(+)-Na+ countertransport were treated with either enalapril (20 mg daily) or hydrochlorothiazide (50 mg daily) during a 30-day period. During the period of enalapril treatment, Na(+)-K+ pump and Na(+)-K(+)-Cl- cotransport increased significantly from 4,282 +/- 255 to 5,236 +/- 325 mumol/l red blood cell/hr (p less than 0.01) and 166 +/- 21 to 220 +/- 24 mumol/l red blood cell/hr (p less than 0.05), respectively. Mean intracellular Na+ content in erythrocytes decreased from 11.4 +/- 0.40 to 10.0 +/- 0.33 mmol/l (p less than 0.01) and exchangeable Na+ from 39.8 +/- 0.6 mmol/kg to 35.6 +/- 0.6 mmol/kg (p less than 0.001). Sodium reduction correlated with the recovery of Na(+)-K(+)-Cl- cotransport activity (r = -0.65, p less than 0.01). During treatment, systolic and diastolic blood pressures were reduced significantly (p less than 0.01). In 12 patients treated with hydrochlorothiazide, Na(+)-K(+)-Cl- cotransport, Na(+)-K+ pump, Na(+)-Li+ countertransport, and Na+ permeability did not change significantly while Na+ content decreased from 11.7 +/- 0.3 to 10.3 +/- 0.2 mmol/l (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Canrenone: an effective antihypertensive in an experimental model of hypertension in which the active transport of sodium is diminished

Recent studies in essential hypertensive patients and rats with genetic hypertension strongly suggested that the development of primary hypertension results from a transient and chronic "cascade" of events; I) excess Na+ intake, II) secretion of natriuretic factors, III) abnormal cell Na+ homeostasis in the vascular wall, due to the presence of inherited and induced abnormalities in different Na+ transport system and IV) increase in cytosolic free Ca2+ content and sympathetic drive. In vitro studies have previously shown that canrenone, an antihypertensive antialdosterone drug, behaves like a partial agonist at the digitalis-receptor site of the Na+, K+-pump. In particular, it has been shown that canrenone counterbalances the increases in internal Na+ and cytosolic free Ca2+ contents induced by ouabain in cultured smooth muscle cells. We thus investigated the effect of canrenone administration in a model of experimental hypertension with increased endogenous "ouabain-like" factors (rats with reduced renal mass under excess Na+ intake: RRM-salt rats). Results presented here confirm that RRM-salt rats exhibit: volume expansion, strongly decreased plasma renin activity, increased endogenous "ouabain-like" factors and (IV) decreased Na+, K+-pump activity and increased Na+ content in erythrocytes. In addition, we found that canrenone is antihypertensive in this model and this is associated with a tendency to normalize volume expansion, plasma levels of endogenous "ouabain-like" factors, Na+, K+-pump activity and Na+ content in erythrocytes. In conclusion, our results suggest that administration of canrenone to RRM-salt rats may induce a lowering of blood pressure by antagonism with endogenous "ouabain-like" factors at the vascular wall.     

Sodium transport parameters in erythrocytes of patients with primary aldosteronism

Primary aldosteronism is an uncommon cause of hypertension but one of particular interest because of its distinctive pathophysiological mechanism of blood pressure elevation. Aldosterone has been associated with increased Na+,K+-adenosine triphosphatase (ATPase) activity, but there is controversy over which sodium transport parameters are responsible for this increase. We measured intracellular sodium, ouabain-sensitive and ouabain-insensitive sodium efflux, and the number of Na+,K+-ATPase sites of washed erythrocytes, as well as Na+-Li+ countertransport and the Li+-K+ cotransport rate constant of lithium-loaded red blood cells (RBCs) in six patients with primary aldosteronism and in 50 normal subjects. Ouabain-sensitive sodium efflux was significantly (p less than 0.001) higher for the primary aldosteronism patients than for normal subjects (1.85 +/- 0.29 vs 1.51 +/- 0.21 mmol/L RBC/hr) even though the intracellular sodium concentration (7.2 +/- 1.5 vs 6.7 +/- 1.9 mM) and the number of the Na+,K+-ATPase sites per RBC (331 +/- 52 vs 385 +/- 97) were not increased. The elevated sodium efflux appeared to be due to a significant (p less than 0.001) increase in the rate constant (1.60 +/- 0.12 x 10(-15) vs 1.28 +/- 0.15 x 10(-15) mmol/site/hr) of the ouabain-sensitive sodium efflux. The rate constant decreased significantly (p less than 0.01) after treatment.     

Erythrocyte sodium fluxes, ouabain binding sites, and Na+,K(+)-ATPase activity in hyperthyroidism

Erythrocyte sodium pump activity, in contrast to other tissues, is decreased in hyperthyroidism. In order to examine whether the effect of thyroid hormones on erythrocytes is part of a generalized effect on other transport pathways, we measured sodium pump activity, Na+,K(+)-adenosine triphosphatase (ATPase) activity, ouabain binding sites, bumetanide-sensitive sodium potassium cotransport (SPC), sodium lithium countertransport (SLC), and ouabain- and bumetanide-insensitive passive efflux of sodium (sodium "leak") in erythrocytes from 20 healthy subjects and 18 untreated hyperthyroid subjects. Sodium pump activity (ouabain-sensitive sodium efflux rate constant), Na+,K(+)-ATPase activity, and the number of ouabain binding sites were lower and the erythrocyte sodium content was higher in hyperthyroid subjects. The rate constants of erythrocyte SPC (P less than .05), SLC (P less than .001), and sodium "leak" (P less than .05) were also significantly lower in hyperthyroidism. In 11 of the hyperthyroid subjects, sodium flux measurements were repeated after 20 weeks of treatment. Sodium pump activity, the number of ouabain binding sites, and the rate constant for SLC increased. These results suggest that the effect of thyroid hormones on the erythrocyte sodium pump is part of a generalized effect on membrane proteins, rather than a specific effect.     

Blood pressure and erythrocyte Na+ transport systems in a French urban male population

This paper reports an investigation of blood pressure (taken as a continuous variable) as a function of: erythrocyte Na+ content; Na+,K+ pump; Na+,K+ cotransport and Na+,Li+ countertransport fluxes, and passive cation permeabilities in fresh erythrocytes from 129 French males who were living in an urban area and were not under treatment for any medical condition (after allowing for the effects of age, body mass index, alcohol and tobacco consumption). In contrast with previous findings in a North American population, we were unable to confirm that blood pressure was correlated with erythrocyte Na+ content and Na+,K+-AT-Pase activity. Conversely, the only transport parameter correlated (negatively) with blood pressure was outward Na+,K+ cotransport [r = -0.20, P less than 0.05 and r = -0.19, P less than 0.05, for systolic (SAP) and diastolic arterial pressure (DAP), respectively; n = 114]. When allowing for age, body mass index and alcohol consumption, the correlation coefficient between the Na+,K+ cotransport system and blood pressure increased from -0.20 to -0.28 (P less than 0.01) for SAP and from -0.19 to -0.28 (P less than 0.01) for DAP (n = 105). We conclude that the correlations between blood pressure and erythrocyte Na+ transport function could differ between North American and French (or Mediterranean) populations. In any case, a decreased pump or outward Na+,K+ cotransport activity may lead hypertensive subjects to a similar increase in cell Na+ (and Ca2+) content in the vascular wall.     

Red blood cell Na+,K+-ATPase in men with newly diagnosed or previously treated essential hypertension

Alterations of cellular function of Na+,K+-adenosine triphosphatase (ATPase; Na+-K+ pump) have been implicated in the pathophysiology of essential hypertension. Therefore, this aspect of red blood cell (RBC) Na metabolism was studied in black men with newly diagnosed, untreated essential hypertension (NEH) and a normotensive control group. RBC Na content, Na+-K+ pump number (ouabain binding sites), and pump activity were measured. No statistically significant differences were found between the two groups for any of these three parameters. However, a group of previously treated essential hypertensive subjects (PEH) who had been withdrawn from therapy in the preceding 6 weeks were also studied. This group differed significantly from the NEH subjects in regard to all RBC Na+-K+ pump parameters. Their RBC Na content (10.27 +/- 3.23 vs 7.77 +/- 2.52 mmol Na/LRBC; p = 0.006) was higher, and their Na+-K+ pump activity (166 +/- 50 vs 221 +/- 87 nmol inorganic phosphate/mg membrane protein/hr; p = 0.03) and Na+-K+ pump number (213 +/- 40 vs 284 +/- 85 binding sites/RBC; p = 0.001) were lower compared with those in NEH subjects. Although the PEH subjects were older and somewhat less hypertensive than their NEH counterparts, these factors were not found to influence the Na+-K+ pump parameters. These results indicate that chronic diuretic therapy of patients with essential hypertension is associated with a reduced number of RBC Na+-K+ pumps. Since RBCs are not considered target cells for diuretics, the effects of these drugs on RBC electrolyte metabolism may occur at the time of erythropoiesis by the production of RBCs with fewer Na+-K+ pumps.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic hypertension in the SHR rat and circulating digitalis compounds

Circulating digitalis-like compounds have been found elevated in some experimental sodium--and volume--dependent hypertensions, as well as in human essential hypertension. As few studies have been undertaken to assess their enhancement in the genetic hypertension of Okamoto (SHR) we have investigated their presence in plasma using 4 criteria: their apparent immunoreactivity with antidigoxin antibodies, their competition with tritiated ouabain binding to the sodium pump of human red blood cells,-their ability to inhibit the Na+, K+ ATPase activity of rat kidney membranes, and the Na+ fluxes from rat red blood cells. When compared to ordinary Wistar (W) and Wistar Kyoto rats (WKY), SHR exhibited a markedly enhanced apparent immunoreactivity with antidigoxin-antibodies (138 +/- 8; 59 +/- 3; 61 +/- 4 pg/ml, n = 15, 6 et 15, p less than 0.001, and p less than 0.001 respectively). The inhibition of ouabain binding by plasma extracts of the three strains did not differ (10.3 +/- 1.6, 9.9 +/- 1.7 and 12.9 +/- 1.4 ng/ml, n = 9, 18 and 14 respectively). When compared to WKY, SHR plasma extracts inhibited the renal Na+, K+ ATPase activity (75.6 +/- 2.6 vs 89.3 +/- 2.4 mumoles Pi . mg-1 . h-1, n = 11 and 10, p less than 0.01, respectively). When incubated in SHR plasma for one hour, net sodium effluxes from Wistar erythrocytes were inhibited compared to that measured in the presence of W or WKY plasma: (5.91 +/- 0.20 vs 7.68 +/- 0.25 and 7.52 +/- 0.15 mmol/l cells, n = 5, 3 and 5, p less than 0.001, and p less than 0.001 respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Aldosterone reduces baroreceptor discharge in the dog.

We have previously demonstrated that baroreceptor discharge sensitivity is depressed in dogs with experimental heart failure and that this depressed sensitivity can be reversed by the Na+,K(+)-ATPase inhibitor ouabain. This suggests that enhanced Na+,K(+)-ATPase activity in baroreceptors is responsible for the blunted baroreceptor discharge sensitivity seen in heart failure state. Because aldosterone, a known stimulator of Na+,K(+)-ATPase, is elevated in heart failure the present study was undertaken to determine the effects on baroreceptor discharge of perfusion of the carotid sinus with aldosterone in normotensive dogs. Single unit baroreceptor activity was recorded as well as carotid sinus pressure and the diameter of the carotid sinus. Perfusion of the carotid sinus with aldosterone (in Krebs-Henseleit solution) significantly elevated threshold pressure (108.5 +/- 3.1 mm Hg versus 92.7 +/- 4.6 mm Hg, p less than 0.05) and reduced peak discharge rate (40.3 +/- 3.9 spikes/sec, p less than 0.05). These effects appeared 15 minutes after aldosterone perfusion and remained constant for the next 60 minutes. There was no change in the carotid sinus pressure-diameter curve during perfusion with aldosterone. Perfusion of the carotid sinus with ouabain (0.1 microgram/ml) during aldosterone perfusion did not reverse the blunted baroreceptor discharge. The blunted baroreceptor activity induced by perfusion of the carotid sinus with aldosterone was prevented by removal of the endothelial cells in the carotid sinus area with a balloon-tipped catheter or by perfusion with saponin. Finally, perfusion of the carotid sinus with spironolactone (10 ng/ml), a mineralocorticoid receptor antagonist, prevented the inhibitory effect of aldosterone. These data suggest that aldosterone reduces maximum baroreceptor discharge.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electrolyte transport across the pleura of rabbits.

The amounts of Na+ and Cl- in the right pleural space of anesthetized rabbits were determined 10 and 60 min after a 2 ml hydrothorax with the following solutions: Ringer, Ringer with an inhibitor of the Na(+)-Cl- coupled transport or of the Na+/K+ pump, Ringer with gluconate instead of Cl- or with methylglucamine instead of Na+. During the 10-60 min period: (a) with Ringer Na+ and Cl- decreased (P less than 0.01) along with an iso-osmotic liquid absorption, (b) with disulfonic-stilbene (0.1 mM), amiloride (0.7 mM), acetazolamide (0.1 mM), or ouabain (0.5 mM) Na+ did not change and Cl- decreased less (P less than 0.01) than with Ringer. With gluconate-Ringer or methylglucamine-Ringer the liquid flow reversed: in the former case Cl- and, to a smaller extent, Na+ increased (P less than 0.01); in the latter only Na+ increased (P less than 0.01). These findings suggest: (1) the occurrence of a Na+/H+ and Cl-/HCO3- double exchange on the serosal side and of a Na+/K+ pump on the interstitial side of the pleural mesothelium; (2) a slow efflux from the pleural space of gluconate or methylglucamine relative to the corresponding influx of Cl- or Na+, respectively; this drags liquid into the space by osmotic gradient.     

3H]ouabain binding of red blood cells in whites and blacks

In a previous study, we demonstrated that the red blood cell Na+ concentration and Na+,K+-ATPase activity are sex-dependent and race-dependent: a higher intracellular Na+ concentration in blacks and men was associated with a lower Na+,K+-ATPase activity. To examine whether the low Na+,K+-ATPase activity is due to a decreased number of enzyme units, altered structure of the enzyme, or the presence of an endogenous digoxinlike substance, ouabain binding studies were performed on the same subject group. The measurements included displacement of [3H]ouabain from its specific binding sites by unlabeled ouabain or potassium. The results demonstrate that groups with lower enzyme activity manifest lower numbers of total specific ouabain binding sites on the surface of the red blood cell (mean +/- SD: blacks, 654 +/- 24.4; whites, 806 +/- 18.3; women, 806 +/- 26.9; men, 728 +/- 21.2). Other kinetic parameters of [3H]ouabain displacement appear to be the same among the groups. The respective red blood cell Na+ and K+ concentrations were negatively and positively correlated with the number of ouabain binding sites. Our findings suggest that the lower activity of red blood cell Na+,K+-ATPase in blacks and men is a function of a lower number of Na+-K+ pump units. The results also indicate that sex and race should be considered when red blood cell ouabain binding is examined.     

Erythrocyte membrane lipids and cationic transport systems in men.

OBJECTIVE: The relationship between erythrocyte membrane and plasma lipids and various transmembrane erythrocyte cationic fluxes was examined in 53 normal men. DESIGN: Different measurements of erythrocyte transport systems were obtained: Na(+)-Li+ countertransport activity; Na+, K+ cotransport activity; Na+, K(+)-ATPase pump activity and the ground membrane permeability for Na+ and K+ as well as the intra-erythrocyte Na+, K+ and Mg2+ concentrations. Plasma cholesterol, triglycerides, phospholipids, free fatty acids, low- and high-density lipoprotein cholesterol levels and the erythrocyte membrane contents of cholesterol, phospholipids and free fatty acids were obtained from fasting subjects. RESULTS: In single regression analysis the erythrocyte Na(+)-Li+ countertransport and Na+, K+ cotransport activities were negatively related to the erythrocyte membrane cholesterol, phospholipids and free fatty acids contents. The Na+, K(+)-ATPase pump activity as assessed by the ouabain-sensitive Na+ efflux was also inversely related to the membrane cholesterol and phospholipids contents. In multiple regression analysis the red blood cell Na(+)-Li+ countertransport activity was independently and negatively related to the membrane cholesterol and free fatty acids contents. CONCLUSION: Our data show that an elevated level of erythrocyte membrane lipids in normal men is accompanied by lower Na(+)-Li+ countertransport, Na+, K+ cotransport and Na+, K(+)-ATPase pump activities.     

The effect of sodium depletion and potassium loading on cortisol induced hypertension in sheep

Glucocorticoid induced hypertension has been regarded as independent of sodium (Na), in contrast to mineralocorticoid induced hypertension, which is Na+-dependent. These studies compare the effect of Na+ depletion and potassium (K+) loading on glucocorticoid hypertension induced by cortisol in conscious sheep. Cortisol (480 mg/d) for 5 days, in sheep on a normal chaff diet (90-140 mmol/d Na+, 200-250 mmol/d K+) increased mean arterial pressure by 18 mmHg on day 5, increased plasma Na+ concentration, reduced plasma K+ concentration, and did not change urinary Na+ excretion. Following Na+ depletion (Na+ loss 603 +/- 49 mmol), cortisol increased mean arterial pressure from 70 +/- 1 mmHg to 76 +/- 3 mmHg on day 5 (P less than 0.001) and the increase in pressure was significantly less than the increase seen on the normal diet (P less than 0.05). Plasma Na+ increased and plasma K+ decreased. Urinary Na+ and K+ excretion was unchanged. KCl loading (700-900 mmol/day) for 10 days had no effect on the maximum rise in mean arterial pressure (+18 mmHg with cortisol in K+ loaded sheep). Plasma Na+ and K+ fell, and urinary Na+ excretion increased during the infusion. These studies show that Na+ depletion, but not KCl loading, reduced cortisol induced hypertension in sheep. These data show that glucocorticoid hypertension is not independent of Na+ status.     

Effects of a chronic high salt intake on blood pressure and the kinetics of sodium and potassium transport in erythrocytes of young and adult subtotally nephrectomized Sprague-Dawley rats

Erythrocyte Na+ and K+ transport mediated by the Na(+)-K+ pump, the Na+,K+ cotransport system and cation leaks, together with blood pressure, were determined in young and adult rats subjected to either chronic salt deprivation or chronic salt loading combined with subtotal nephrectomy. The kinetics of ion transport were studied in Na+ media as a function of extracellular K+, replaced by extracellular Rb+, and intracellular Na+ varied around the physiological range. A high salt intake increased blood pressure in young but not in adult subtotally nephrectomized rats. Erythrocyte Na+ or K+ contents of salt-deprived and salt-loaded rats did not differ. There were no major changes in Na+,K+ cotransport or cation leaks in salt-loaded rats. Chronic salt loading caused some alterations in the kinetics of the Na(+)-K+ pump, which were greater in young than in adult rats. The most pronounced change was a decreased affinity of the Na(+)-K+ pump for intracellular Na+, which was partially balanced by an increased maximal velocity. At physiological (in vivo) ion concentrations these kinetic alterations caused a slight reduction in total ouabain-sensitive Rb+ uptake [partly due to a decrease in intracellular K+:extracellular Rb+ (1:1) exchange] but no changes in Na+ net extrusion in salt-loaded rats. The erythrocyte Na+ and K+ transport systems showed no changes in intrinsic properties that would favour the development or maintenance of salt hypertension in young over adult rats if similar alterations occurred in tissues relevant for blood pressure control.     

Red cell membrane Na+ transport systems in hereditary spherocytosis: relevance to understanding the increased Na+ permeability

Red blood cells (RBCs) in hereditary spherocytosis (HS) show high sodium (Na+) and potassium (K+) movement across the membrane, resulting in dehydration. In general, these abnormal cation fluxes have been interpreted as "increased leaks" due to passive or electrodiffusional permeability of the RBC membrane. A study to elucidate the contribution of concomitant ouabain-resistant pathways (Na-K-2Cl cotransport and Na-Li countertransport) to abnormal Na+ permeability present in RBCs of subjects with HS has been undertaken. Accordingly, erythrocyte Na+ and K+ content and transmembrane cation movements via the Na-K pump, Na-K-2Cl cotransport, Na-Li countertransport, and Na+ passive diffusion, were measured in 25 non-splenectomized patients with HS and compared with the results obtained from the study of 11 patients with congenital non-spherocytic haemolytic anaemia (CNSHA) due to hereditary elliptocytosis (7 cases) and RBC enzyme defects (4 cases) and of 30 normal controls. Compared to the controls, patients with HS exhibited a highly significant (P<0.001) increase in all the Na+ transmembrane movements via passive diffusion (411+/-243 vs 105+/-40), Na-K pump (2615+/-970 vs 1874+/-359), Na-K-2Cl cotransport (males: 371+/-138 vs 190+/-42; females: 401+/-134 vs 104+/-44) and Na-Li countertransport (207+/-131 vs 98+/-41). This was associated with increased Na+ and decreased K+ content, resulting in a reduction of total cation (Na+ + K+) RBC concentration. Furthermore, significant correlations were also found between the patients' RBC cationic content and the mean corpuscular haemoglobin concentration (MCHC) (r=0.51, P<0.05) and between the Na+ passive leak and the haematocrit value (r=-0.44, P<0.05). In the patients with CNSHA, a less significant (P<0.01) increase of active (Na-K pump) and passive (leak) transmembrane permeability to Na+ was associated with normal transmembrane movements via Na-K-2Cl cotransport and Na-Li countertransport. The present study demonstrates that in HS, RBCs are characterized by a variable, but always significant increase of all the membrane transport systems leading to the extrusion of Na+, and that these abnormalities, regardless of their relation to membrane structural defects, may probably be valuable for the differential diagnosis between HS and other congenital defects of RBCs.