Erythrocyte cation transport systems and plasma lipids in a general male population

The relationships between five erythrocyte cation transport systems (Na(+)-K+ pump, Na(+)-K+ cotransport, Na(+)-Li+ countertransport and Na+ and K+ passive permeabilities) and plasma lipids (total plasma cholesterol, high-density lipoprotein cholesterol and triglycerides) were investigated in 129 male adult subjects with no known history of hypertension. Na+ and K+ erythrocyte contents were also considered for their possible relationships with plasma lipids. Na(+)-K+ cotransport and passive Na+ permeability were both significantly correlated with plasma triglycerides. Conversely, no significant correlation was found between erythrocyte cation transport systems or erythrocyte cation contents and total cholesterol. These findings suggest that plasma lipids can modulate erythrocyte ion transport activity in the general population.     

The characteristics of erythrocyte Na+ transport systems in normal pregnancy and pregnancy-induced hypertension.

OBJECTIVE: To assess the role Na plays in the pathogenesis of pregnancy-induced hypertension (PIH). METHODS: We assessed Na and K content, the maximum number of ouabain binding sites, Na(+)-Li+ countertransport and Na(+)-K+ cotransport in erythrocytes from women with untreated PIH, normal pregnant women and healthy non-pregnant women. RESULTS: In normal pregnancy, the Na content of erythrocytes decreased, accompanied by the activation of Na excretion systems. In women with PIH, the Na content of erythrocytes and the Na(+)-K+ cotransport activity significantly increased, whilst erythrocyte K content and the maximum number of ouabain binding sites significantly decreased, compared with observations in normal pregnancy. In both normal pregnancy and PIH, there were no differences in Na(+)-Li+ countertransport. CONCLUSIONS: These results suggest that the increase of erythrocyte Na content in women with PIH may be contributed to by a reduction in the number of ouabain binding sites, whilst Na(+)-K+ cotransport and Na(+)-Li+ countertransport may compensate for this effect in women with PIH.     

Is there increased cardiovascular risk in essential hypertensive patients with abnormal kinetics of red blood cell sodium-lithium countertransport?

Na+ transport kinetics were studied in red blood cells (RBCs) from 50 essential hypertensive patients and 30 normotensive controls. Seven hypertensive patients were characterized by the following: (1) a maximal rate of Na+-Li+ countertransport higher than an upper normal limit of 525 mumol.litre cells-1.h-1; (2) an apparent dissociation constant for internal Na+ higher than an upper normal limit of 20.4 mmol.litre cells (in only five of the seven hypertensives); (3) no other kinetic abnormality in Na+,K+ pump, Na+,K+ cotransport or passive Na+ permeability. Clinically, hypertensives with abnormal countertransport were characterized by high serum low-density lipoprotein (LDL) cholesterol levels and the presence of electrocardiographic left ventricular hypertrophy (LVH). Conversely, mean values of these two clinical parameters were normal in the remaining hypertensive patients, independently of the presence of other abnormalities in Na+,K+ pump, Na+,K+ cotransport or passive Na+ permeability. In conclusion, the presence of abnormal Na+-Li+ countertransport kinetics in erythrocytes may be associated with an enhanced cardiovascular risk in hypertension.     

Erythrocyte and platelet fatty acids in retinitis pigmentosa

The fatty acid composition and the glutathione-peroxidase activity (GSH-Px) of erythrocytes and platelets, the production of malondialdehyde (MDA) by platelets and the activity of the main systems of transmembrane cation transport in erythrocyte have been studied in 12 patients (5 males and 7 females) affected by retinitis pigmentosa (RP). A remarkable increase of saturated fatty acids (SFA), particularly of stearic acid (C18:0), has been noted in these patients. The reduced unsaturated/saturated fatty acids ratio (PUFA/SFA) observed in both erythrocytes and platelets and the decrease of arachidonic acid in platelets may depend by an active peroxidation process as documented by the increase of MDA. Platelet glutathione-peroxidase (PTL-GSH-PX) and plasma retinol were in the normal range, whereas erythrocyte glutathione-peroxidase (E-GSH-PX), MDA and plasma alfa-toco-pherol were increased in patients with RP. The activities of Na(+)-K+ pump, cotransport and Na(+)-Li+ countertransport were normal in RP erythrocytes.     

Influence of race, sex, and blood pressure on erythrocyte sodium transport in humans

Sodium transport of erythrocytes from normotensive and essential hypertensive subjects was evaluated by determining ouabain-sensitive and ouabain-insensitive sodium efflux rates, Na+-Li+ countertransport rates, Li+-K+ cotransport rate constants (lithium replacing sodium), intracellular sodium concentrations, and the number of Na+,K+-adenosine triphosphatase (ATPase) sites per erythrocyte. Subjects included men and women, blacks and whites. Hypertensive subjects had significantly higher sodium transport than did normotensive subjects for ouabain-sensitive sodium efflux (p less than 0.025) and Na+-Li+ countertransport (p less than 0.001). Sexual differences were noted for ouabain-sensitive (p less than 0.001) and ouabain-insensitive (p less than 0.001) sodium efflux, for intracellular sodium concentration (p less than 0.025), and for the Li+-K+ cotransport rate constant (p less than 0.005), all with higher values for men than for women. Racial differences were noted for ouabain-insensitive sodium efflux (p less than 0.005), Na+-Li+ countertransport (p less than 0.001), and the Li+-K+ cotransport rate constant (p less than 0.001); values were higher in whites than blacks for all three measurements. The number of [3H]ouabain binding sites was lower for blacks (p less than 0.001) and the intracellular sodium concentration was higher for blacks (p less than 0.001). Among all subjects, significant (p less than 0.001) correlations were found between intracellular sodium concentration and the number of Na+,K+-ATPase sites per erythrocyte (r = -0.78) and between the ouabain-sensitive sodium efflux per site and intracellular sodium concentration (r = 0.85, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Disturbances in Na+ Transport Systems Induced by Ethanol in Human Red Blood Cells

The effects of ethanol on fluxes catalyzed by four Na+ transport systems (ouabain-sensitive Na+, K+ pump, bumetanide-sensitive Na+, K+ cotransport system, Na+:Li+- countertransport and anion carrier) and on Na+ and K+ leaks were investigated in human red blood cells. Ethanol concentrations higher than 32 mM were required in order to significantly modify erythrocyte Na+ transport function. The observed changes can be summarized as follows: (a) stimulation of Na+ efflux through the Na+, K+ pump (by 21-32% at 160-400 mM) and Na+:Li+ countertransport (by 34-59% at 160-400 mM); (b) inhibition of outward Na+, K+ cotransport (by 23-34% at 160-400 mM) and LiCO3- influx through the anion carrier (by 17-21% at 64-400 mM); and (c) increase in Na+ and K+ leaks (by 13-16% at 64-400 mM). The effects of ethanol on the Na+,K+ pump and Na+,K+ cotransport system resulted from changes in maximal rates of Na+ efflux (increased and decreased, respectively) without any significant effect on the apparent affinities for internal Na+. Erythrocytes preincubated for 1 hr with 160 mM ethanol, washed and further incubated in flux media, recovered a normal Na+ transport function. In conclusion, high concentrations of ethanol induced reversible perturbations of fluxes catalyzed by erythrocyte Na+ transport systems. The observed effects may reflect disturbances in Na+ transport function associated with severe intoxication.     

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.     

Platelet and erythrocyte Mg2+, Ca2+, Na+, K+ and cell membrane adenosine triphosphatase activity in essential hypertension in blacks.

OBJECTIVE: To assess the relationship between intracellular Mg2+, Ca2+, Na+ and K+ and cell membrane adenosine triphosphatase (ATPase) activity in normotensive and hypertensive blacks. DESIGN: Intracellular cations and cell membrane ATPase activity were studied in black patients with untreated essential hypertension and age-, weight- and height-matched normotensive controls. Platelet, erythrocyte and serum Mg2+, Ca2+, Na+ and K+ levels as well as platelet and erythrocyte membrane Na+,K(+)-ATPase, Ca(2+)-ATPase and Mg(2+)-ATPase activities were measured in all subjects. METHODS: Intracellular Na+ and K+ were measured by flame photometry and Mg+ and Ca+ by atomic absorption spectrophotometry. Cell membrane ATPase activity was determined by a colorimetric method. RESULTS: The hypertensive group consistently demonstrated depressed activity of each ATPase studied, with significantly lower serum Mg2+, serum K+, erythrocyte Mg2+ and platelet Mg2+ levels compared with the normotensive group. Platelet Na+ and Ca2+ and erythrocyte Ca2+ were significantly elevated in the hypertensive group. In the hypertensive group, mean arterial pressure (MAP) was inversely correlated with platelet and erythrocyte membrane Na+,K(+)-ATPase, Ca(2+)-ATPase and Mg(2+)-ATPase. Serum Mg2+, serum Ca2+ and platelet Mg2+ were negatively correlated with MAP in the hypertensive group whilst erythrocyte and platelet Ca2+ were positively correlated. In the normotensive group, platelet Mg2+ and MAP were negatively, and erythrocyte Ca2+ and MAP, positively correlated. CONCLUSIONS: Black patients with essential hypertension have widespread depression of cell membrane Na+,K(+)-ATPase, Ca(2+)-ATPase and Mg(2+)-ATPase activities with serum and intracellular Mg2+ depletion and cytosolic Na+ and Ca2+ overload, which may reflect an underlying membrane abnormality in essential hypertension. These cellular abnormalities may be related to the defective transport mechanisms that in turn may be aggravated by Mg2+ depletion.     

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)     

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.     

Therapeutic response to canrenone of patients with essential hypertension as a function of sodium transport anomalies and ouabain sensitivity of erythrocytes

The presence of Na+ transport abnormalities (decreased affinity of the Na+/K+ pump or the Na+, K+ cotransport for internal Na+, increased Na+:Li+ countertransport, increased Na+ leak), Na+ content, Na+/K+ pump activity and sensitivity to ouabain were investigated in erythrocytes from 13 patients with essential hypertension. According to the presence or absence of Na+ transport abnormalities, the patients were divided into two groups: TrNa(+) (n = 9) and TrNa(-) (n = 4) respectively. Compared with TrNa(-) patients, TrNa(+) patients were characterized by: (i) a higher arterial pressure (131.4 +/- 11.8 vs 110.0 +/- 13.2 mmHg, p less than 0.05), (ii) an increased erythrocyte Na+ content (8.9 +/- 1.0 vs 6.3 +/- 0.8 mmol/l.cells, p less than 0.01) associated with (iii) a decreased rate constant of Na+/K+ pump activity (235 +/- 26 vs 309 +/- 45 h-1, p less than 0.05) and (iv) a higher sensitivity to ouabain (0.76 +/- 0.23 vs 1.12 +/- 0.26 microM, p less than 0.05). Oral administration of canrenone 50 mg per day during 7 weeks decreased mean arterial pressure by 10-30 mmHg in 6 out of the 9 TrNa(+) patients. Conversely, it decreased mean arterial pressure in only one out of the 4 TrNa(-) patients. The hypotensive effect of canrenone in TrNa(+) patients was not associated with normalization of their Na+/K+ pump activity. Canrenone did not modify the sensitivity to ouabain of either the TrNa(+) or the TrNa(-) patients. Before treatment, acute injection of ouabain provoked an inhibition of the erythrocyte Na+/K+ pump, without any change in Na+ content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Membrane ion transport in erythrocytes of salt hypertensive Dahl rats and their F2 hybrids: the importance of cholesterol.

The possible association of salt hypertension and altered lipid metabolism with abnormalities of particular systems transporting sodium and potassium has been studied in erythrocytes of Dahl rats and their F2 hybrids fed a high-salt diet since weaning. Our attention was paid to the Na(+)-K+ pump, Na(+)-K+ cotransport and especially to passive membrane permeability for Na+ and Rb+ (Na+ and Rb+ leak), because the Na+ leak was found to be dependent on the genotype, age and salt intake of Dahl rats, whereas the Rb+ leak was suggested to be a potential marker of salt sensitivity in Dahl and Sabra rats. Young male Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats kept on a low-salt (0.3% NaCl) or high-salt diet (8% NaCl) were used for the progenitor study. The subsequent genetic study was based on 135 young male SS/Jr x SR/Jr F2 hybrids fed a high-salt diet since weaning. Ouabain (5 mmol/l) and bumetanide (10 micromol/l) were used to distinguish the contribution of the Na(+)-K+ pump, Na(+)-K+ cotransport and passive membrane permeability to measured net Na+ fluxes and unidirectional Rb+ (K+) movements. Compared to normotensive SR/Jr animals, salt-loaded SS/Jr rats had higher blood pressure (BP), elevated erythrocyte Na+ content, and increased Na+ and Rb+ leaks together with enhanced Na+ and Rb+ transport mediated by the Na(+)-K+ pump and Na(+)-K+ cotransport system. Salt hypertensive Dahl rats were also characterized by elevated plasma levels of total cholesterol and triglycerides, which were positively associated with BP of F2 hybrids (r=0.27 and 0.24, p< 0.01). In F2 hybrids, mean arterial pressure correlated significantly with erythrocyte Na+ content (r=0.24, p<0.01) and ouabain-sensitive Na+ extrusion, but not with the passive membrane permeability for Na+ or Rb+ (r=-0.02 and 0.06, not significant). Both of the above-mentioned significant associations could partially be ascribed to the dependence of erythrocyte Na+ content and ouabain-sensitive Na+ extrusion on plasma cholesterol (r=0.18 and 0.21, p<0.05). Our results support the idea that abnormal lipid metabolism and/or altered Na+,K(+)-ATPase function play an important role in the pathogenesis of salt hypertension in salt-sensitive Dahl rats.     

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.     

Chronic Alcohol Intake Induces Reversible Disturbances on Cellular Na+ Metabolism in Humans: Its Relationship with Changes in Blood Pressure

The effect of chronic alcohol consumption on Na(+)-K+ ATPase, Na(+)-Li+ countertransport, outward Na(+)-K(+)-Cl- cotransport system and the Na+ leak was investigated in red blood cells from 18 normotensive subjects with a daily alcohol intake of more than 150 g. The study was repeated after 3 months of alcohol withdrawal, and results were compared with a group of 20 healthy normotensive teetotalers. Maximal efflux rate (Vmax) and apparent dissociation constant for internal Na+ (KNa) of the Na(+)-K+ pump and the Na(+)-Li+ countertransport were significantly higher in alcohol consumers. A positive correlation between daily alcohol intake and Vmax of both transport systems (p less than 0.05) was observed. These values significantly decreased after alcohol withdrawal. A simultaneous stimulation of the Na(+)-K(+)-Cl- cotransport system after alcohol withdrawal was also observed. Blood pressure values were higher in alcoholics (133.7/82.3) than in abstainers (121.4/75 mmHg) and significantly decreased (128.5/76.9 mmHg) after withdrawal. A positive correlation between the stimulation of the Na(+)-K(+)-Cl- cotransport and the decrease of blood pressure after withdrawal was observed. In conclusion, chronic alcohol intake induces disturbances on red blood cell Na+ metabolism that dissipate with the cessation of drinking. Similar abnormalities also reported in humans and animals with primary hypertension have been associated in the pathogenesis of essential hypertension. Therefore, the pressor effect of chronic alcohol intake could be mediated through these changes in cellular Na+ metabolism.     

Effect of dietary fats on erythrocyte membrane lipid composition and membrane-bound enzyme activities.

Four different oil-based diets were used in a feeding study involving rats to assess the relationship between the fatty acid composition of the dietary fat and its influence on erythrocyte membrane (EM) lipid composition and the activities of membrane-bound enzymes. Nutritionally adequate diets containing 20% groundnut (GNO), coconut (CO), safflower (SO), or mustard oil (MO) were fed to weanling CFY rats for 4 months. EMs were analyzed for total cholesterol, phospholipids, fatty acid profiles, and sialic acid content. Activities of membrane-bound enzymes such as Na+, K(+)-adenosine triphosphatase (ATPase), Mg(2+)-ATPase, Ca2+, Mg(2+)-ATPase, and acetylcholinesterase were also assayed. The activities of all membrane-bound enzymes, except Mg(2+)-ATPase, and sialic acid content were higher in the MO-fed group than in the rest of the groups. Ca2+, Mg(2+)-ATPase activity was distinctly lower in the SO-fed group than in the other groups. Cholesterol to phospholipid molar ratio was similar in all the groups. However, SO- and MO-fed groups displayed an increased cholesterol content and a higher degree of unsaturation in the membrane fatty acid composition. The higher membrane fatty acid unsaturation in the SO-fed group was principally due to linoleic (18:2) and arachidonic (20:4) acids, while in the MO-fed group it was mainly due to oleic (18:1), eicosenoic (20:1), erucic (22:1), and linoleic (18:2) acids. These results suggest a relationship between the quality of dietary fat, EM fatty acyl composition, and the activities of membrane-bound enzymes.     

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.     

Erythrocyte and leucocyte sodium and potassium transport systems during long-term diuretic administration in men

The effect of xipamide on the intracellular concentration and transmembrane fluxes of Na+ and K+ was studied in 12 normal male subjects, using a double-blind cross-over design. After a run-in period on placebo for 1 week, the subjects were treated with either placebo (n = 6) or xipamide 20 mg once a day (n = 6) for 16 weeks and were then switched to the alternative medication for another 16 weeks. The intra-erythrocyte and intra-leucocyte Na+ concentration was increased by 11 and 7%, respectively, during xipamide administration, while the intracellular K+ concentration was decreased by 3 and 4%, respectively. No significant effect of xipamide could however be demonstrated on the ouabain-sensitive, bumetanide-sensitive or ouabain-bumetanide-resistant 86Rb uptake and on the maximal 3H-ouabain binding in erythrocytes and leucocytes. The red cell Na+-Li+ countertransport was also not changed in the xipamide-treated subjects. Our data suggest that the increased intracellular Na+ concentration and the decreased K+ concentration in red and white blood cells of xipamide-treated subjects cannot be attributed to changes in the activity of the Na+ pump, the Na+-K+ cotransport or Na+-Li+ countertransport system or to changes in the number of active Na+ pump units.     

Na+-H+ exchange and other ion-transport systems in erythrocytes of essential hypertensives and spontaneously hypertensive rats: a comparative analysis

The activity of ion-transport systems and Ca2+-induced erythrocyte haemolysis were compared between patients with essential hypertension and two strains of spontaneously hypertensive rats. Previous data on the increased rate of Na+-Li+ countertransport in erythrocytes of essential hypertensives were confirmed in this study. However, identification of Na+-Li+ countertransport in rat erythrocytes remained a complicated person because of the high rate of sodium-independent efflux of Li+. The rate of Na+-H+ exchange increased by 50-80% both in spontaneously hypertensive Wistar-Kyoto rats (SHR) and in patients with essential hypertension. No difference between Milan hypertensive strain rats (MHS) and Milan normotensive strain rats (MNS) was found. The rate of Na+,K+ cotransport increased in SHR and MHS erythrocytes compared with rats of the control strains [normotensive Wistar-Kyoto rats (WKY) and MNS; 30-50 and 90-110%, respectively]. No difference in this parameter was found between patients with essential hypertension and healthy subjects. Erythrocytes of patients with essential hypertension and of SHR were characterized by a higher sensitivity of their K+ channels to the increased concentration of intracellular Ca2+. This parameter did not change in MHS erythrocytes. Ca2+-induced haemolysis increased four- to fivefold in MHS erythrocytes compared with MNS and did not change in erythrocytes of SHR and patients with essential hypertension. The conclusion from these data is that the SHR strain is a more adequate model of human essential hypertension than the MHS.     

Disparate effects of weight loss on insulin sensitivity and erythrocyte sodium-lithium countertransport activity.

Previous investigations have demonstrated an association between impaired insulin sensitivity and elevated erythrocyte sodium-lithium countertransport (Na(+)-Li+ CT) activity. It has been speculated that insulin resistance and endogenous hyperinsulinemia are causally related to the development of elevated Na(+)-Li+ CT activity. To test this hypothesis, we measured insulin sensitivity (euglycemic insulin clamp technique) and Na(+)-Li+ CT activity in eight obese women before (weight = 102 +/- 5 kg) and after (weight = 88 +/- 5 kg; P < .001) a 10 week weight reduction program. Maximal velocity of Na(+)-Li+ CT activity did not change (0.50 +/- 0.09 v 0.49 +/- 0.10 mmol/L red blood cells/h; P = NS) despite the significant improvement in insulin sensitivity (73 +/- 12 vs 110 +/- 7 mg/m2/min; P < .0025) and reduction in fasting insulin levels (17 +/- 2 v 10 +/- 2 microU/mL; P < .05) that accompanied weight loss. These results suggest that insulin resistance and hyperinsulinemia are not linked pathophysiologically to the development of elevated Na(+)-Li+ CT activity.     

Sodium-lithium exchange and sodium-proton exchange are mediated by the same transport system in sarcolemmal vesicles from bovine superior mesenteric artery

Several laboratories have reported that Na+-Li+ countertransport activities are increased in red blood cells from patients with essential hypertension. It has been proposed that the activity of this red blood cell transport system might reflect the activity of a similar system in vascular smooth muscle. We previously demonstrated Na+-Li+ exchange in sarcolemmal vesicles from canine artery and proposed that this transport function might be mediated by the Na+-H+ exchanger. In the present studies, however, we were unable to demonstrate Na+-Li+ countertransport in canine red blood cells. Since bovine red blood cells have a vigorous Na+-Li+ exchanger and we previously demonstrated Na+-H+ exchange in sarcolemmal vesicles from bovine artery, we wished to determine whether bovine sarcolemmal vesicles mediate Na+-Li+ exchange and whether this transport function is mediated via the Na+-H+ exchanger. We found that an outwardly directed proton or Li+ gradient stimulated 22Na+ uptake in sarcolemmal vesicles from bovine superior mesenteric artery. Li+ gradient-stimulated Na+ uptake was not due to electrical coupling between the two ions, was not affected by a change in membrane potential, and could not be explained by the parallel operation of Li+-H+ and Na+-H+ exchange. External Li+ inhibited proton gradient-stimulated Na+ uptake, and external protons inhibited Li+ gradient-stimulated Na+ uptake. Na+ efflux from vesicles was stimulated by inwardly directed gradients for Li+ or protons, and these effects were not additive. Proton efflux from vesicles was stimulated by inwardly directed gradients for Na+ or Li+, and these effects were not additive. Finally, Na+-H+ exchange and Na+-Li+ exchange in sarcolemmal vesicles were inhibited by 5-(N-ethyl-N-isopropyl)amiloride in an identical dose-dependent manner. In conclusion, Na+-Li+ countertransport could not be demonstrated in canine red blood cells, but as is the case with bovine red blood cells, sarcolemmal vesicles from bovine artery mediate Na+-Li+ countertransport. This transport function and sarcolemmal Na+-H+ exchange are mediated via a single 5-(N-ethyl-N-isopropyl)amiloride-sensitive cation exchanger with affinity for Na+, Li+, and protons. The cow, as opposed to the dog, may be a good animal model to test whether the activity of red blood cell Na+-Li+ countertransport is predictive of the activity of Na+-Li+ (and Na+-H+) exchange in vascular smooth muscle.