Na+, K+ and water balance in young spontaneously hypertensive rats: relationship to blood pressure after high K+ treatment

These studies were designed to investigate the effects of high dietary K+ on electrolyte and water balance in young spontaneously hypertensive rats (SHR) and to relate these effects to changes in blood pressure. The high K+ diet reduced blood pressure by approximately 10 mmHg during the development of hypertension. Blood pressure, however, plateaued at the same maximum level as control by age 13 weeks. Rats fed the high K+ diet showed a significant increase in water intake and urine volume throughout the treatment period but no change in plasma volume or extracellular fluid volume occurred. A slight natriuresis was also observed in rats on the high K+ diet, but this was not of sufficient magnitude to decrease total body Na+. These results confirm previous findings that K+ causes a diuresis and a natriuresis, but demonstrate that the diuretic action of K+ cannot explain its antihypertensive properties in young SHR.     

Direct demonstration of an inhibitor of sodium, potassium dependent adenosine triphosphatase (Na+, K+-ATPase) in plasma from normotensive and hypertensive subjects

An endogenous inhibitor of Na+, K+-ATPase was extracted from human plasma and sera and concentrated by a novel reverse-phase octadecylsilane chromatography method. The active extracts (eluates) were dried and reconstituted in the minimum volume of the non-adsorbed fraction of the plasma from which they had been derived. Reconstituted eluates, non-adsorbed plasma fractions and native plasma samples were then tested for their ability to inhibit phosphate production in standard Na+, K+-ATPase incubation mixtures. In a pilot study 31 samples of pooled normal human sera were assayed. The eluates gave a significantly lower production of phosphate than the non-adsorbed fractions or the native sera (n = 31, p less than 0.0025). Further concentration of the eluates by repeated chromatography increased the inhibitory power of the eluate proportional to the concentration achieved, as quantified by ouabain dose-equivalents. In clinical studies, samples from 12 normotensive subjects and from 12 untreated patients with essential hypertension were tested. Significant inhibition of the ATPase by the eluates, as compared to the corresponding non-adsorbed fractions was seen for samples from both normotensive (p less than 0.05) and hypertensive (p less than 0.05) subjects. There was no significant difference in incidence or degree of inhibition between the normotensive and hypertensive groups. This study provides direct evidence for the presence of an endogenous inhibitor of Na+, K+-ATPase in human plasma.     

Measurement by bioluminescence technique of erythrocyte membrane Na+,K+-ATPase activity in hypertensive patients

Erythrocyte membrane Na+,K+-ATPase activity was measured using a bioluminescence technique in 28 hypertensive patients (24 with essential hypertension, 2 with renovascular hypertension and 2 with hypertension secondary to primary hyperaldosteronism) and in 28 normotensive control subjects matched for age and sex. Erythrocyte Na+,K+-ATPase activity was significantly reduced in the patients with essential hypertension (130.9 +/- 11.4 vs. 186.6 +/- 19.5 nmol ATP/mg prot per h; mean values +/- SEM; p less than 0.05) and in the patients with secondary hypertension. A significant negative correlation was found between erythrocyte Na+,K+-ATPase and systolic blood pressure (r = -0.603; p less than 0.01), but not between Na+,K+-ATPase and plasma renin activity or plasma aldosterone levels. These data confirm the findings of a number of previous studies reporting reduced activity of erythrocyte Na+,K+-ATPase possibly related to the presence of a circulatory inhibitor of sodium pump. The method, based on ATP assay by bioluminescence, presents a high degree of specificity as well as simple, rapid execution.     

Increased renal tubular sodium pump and Na+,K+-adenosine triphosphatase in streptozotocin-diabetic rats

The effects of chronic glucose osmotic diuresis on renal tubular sodium pump and Na+,K+-adenosine triphosphatase (ATPase) activities were studied in chronic streptozotocin-induced diabetic rats. Four to seven weeks after streptozotocin (60 mg/kg i.p.) injection, specific renal Na+,K+-ATPase activity showed a 34.8% increase as compared to the saline-citrate treated controls, whereas the nonspecific Mg++-ATPase was not altered. The concentration of Na+,K+-ATPase, estimated from the maximum [3H]ouabain binding site concentration, also showed a significant increase in the chronic streptozotocin-diabetic rats. To determine further the specificity of this increase in Na+,K+-ATPase, the activity of the sodium pump, estimated from ouabain-sensitive 86Rb uptake, was measured in nonenzymatically isolated renal tubules. Again, a significant (+106.4%) increase in the renal tubular sodium pump activity was observed in the streptozotocin-diabetic rats, whereas the nonspecific, ouabain-insensitive 86Rb uptake was not altered. Neither was there any difference in 86Rb uptake by the isolated renal glomeruli. Thus, it appears that chronic streptozotocin-induced diabetes in rats is associated with a significant increase in renal tubular sodium pump and Na+,K+-ATPase. The latter effects may represent an important physiologic adaptation of the kidneys to maintain electrolyte homeostasis in diabetes.     

Cytochemical localization of Na+, K+-ATPase in the rat hepatocyte.

The enzyme Na+,5+-ATPase was cytochemically localized in the rat hepatocyte by a modification of the Ernst potassium-dependent nitrophenyl phosphatase technique. Measurement of nitrophenol release from 50-micrometer liver slices confirmed the presence of ouabain-inhibitable nitrophenyl phosphatase activity that increased over the 30-min incubation period. Electron micrographs demonstrated that sinusoidal and lateral membrane reaction product deposition was K+-dependent, Mg++-dependent, inhibited by ouabain but not by alkaline phosphatase inhibitors, and was localized to the cytoplasmic side of the membrane. In contrast, canalicular reaction product was K+-independent, Mg++-dependent, inhibited by alkaline phosphatase inhibitors but not by ouabain, and was localized to the luminal side of the membrane. These findings indicate that Na+,K+-ATPase is localized to the sinusoidal and lateral portions of the rat hepatocyte plasma membrane and is not detectable on the bile canaliculus where alkaline phosphatase is confined. This basolateral localization of Na+,K+-ATPase is similar to that found in epithelia where secretion is also directed across the apical membrane.     

Effect of gentamicin treatment on adenylate cyclase and Na+, K+-ATPase activities in renal tissues of rats

Gentamicin (20 mg/kg) treatment of male rats reduced Na+,K+-ATPase activity by 32% in renal cortical plasma membranes. In contrast, adenylate cyclase stimulation by isoproterenol or a guanyl nucleotide or both was enhanced by as much as twofold in glomeruli and in plasma membranes of gentamicin-treated rats. These effects of gentamicin are suggested to be related to the changes in renal phospholipid metabolism produced by the drug.     

Increased intracellular calcium and decreased activities of leucocyte Na+,K+-ATPase and Ca2+-ATPase in asthma.

The present study was carried out to determine the intracellular free calcium concentration ([Ca(2+)](i)) and the activity of its regulatory enzymes (Na(+),K(+)-ATPase and Ca(2+)-ATPase) in leucocytes. Levels of plasma lysophosphatidylcholine (LPC) were also measured. Then the relationship between these parameters and the clinical severity of asthma and bronchial reactivity was studied. Patients with asthma were divided into three groups: acute asthma (subjects in acute exacerbation), uncontrolled asthma (subjects currently symptomatic) and stable asthma (subjects currently asymptomatic). A group of normal subjects was also studied. Spirometry, specific airway conductance and bronchial reactivity measurements were carried out. The following biochemical parameters were studied in venous blood: leucocyte [Ca(2+)](i), Na(+), K(+)-ATPase and Ca(2+)-ATPase activities, and plasma LPC. Leucocyte [Ca(2+)](i) was increased and the activities of Na(+),K(+)-ATPase and Ca(2+)-ATPase were decreased in patients with asthma. Plasma levels of LPC were also increased. These changes were observed to be greatest among asthmatics in acute exacerbation of asthma, and lesser in magnitude in patients with less severe asthma. The activities of both ATPases were found to have a significant positive correlation, and [Ca(2+)](i) and the levels of plasma LPC a significant negative correlation, with predicted forced expiratory volume in 1 s (FEV(1)). No significant correlation was observed between the biochemical parameters and bronchial reactivity. It is concluded that intracellular calcium homoeostasis is abnormal in asthma; specifically, the activities of Na(+),K(+)-ATPase and Ca(2+)-ATPase are decreased. These abnormalities may modulate the clinical severity of asthma.     

Effects of a high K+/low Na+ diet on blood pressure in young spontaneously hypertensive rats

Blood pressure was measured after treatment with a high K+, a low Na+ and a combined high K+/low Na+ diet in young spontaneously hypertensive rats (SHR). A high K+ diet reduced blood pressure by approximately 10 mmHg during the development of hypertension. This decrease was accompanied by a significant increase in water intake and urine volume and a significant decrease in plasma renin activity (PRA). A low Na+ diet also decreased blood pressure significantly, but, in contrast to the high K+ diet, water intake and urine volume significantly decreased and PRA increased. When both diets were given together, the antihypertensive effects of both were eliminated. Thus while an increase in dietary K+ and a decrease in dietary Na+ are both effective antihypertensive regimens in SHR, the mechanism of action of each appears to be different and may be antagonistic in these animals.     

Ion flux and Na+,K+-ATPase activity of erythrocytes and leucocytes in thyroid disease

In hyperthyroidism, erythrocytes show decreased Na+,K+-ATPase activity, decreased [3H]ouabain binding capacity (an index of the number of sodium pumps) and decreased active sodium and potassium flux rates, with a high intracellular sodium concentration. As erythrocytes are non-nucleated and atypical cells, we have studied electrolyte status in thyroid disease using mixed leucocytes as well; the results obtained differed from those in erythrocytes. When compared with findings in healthy subjects, leucocyte Na+,K+-ATPase activity, [3H]-ouabain binding capacity, total and active rubidium (used instead of potassium) influx were all significantly increased in untreated hyperthyroidism and decreased in untreated hypothyroidism. In hyperthyroidism, there was also a decrease in plasma potassium, an increase in sodium efflux rate and efflux rate constant, but no significant changes in cell sodium and potassium concentrations. All these changes returned to normal in successfully treated patients. There was a significant correlation between these abnormalities of electrolyte status and thyroid disease status (as serum thyroid stimulating hormone and free thyroxine).     

Ouabain-specific antibodies: immunochemical properties and reversal of Na+, K+-activated adenosine triphosphatase inhibition

Antibodies with high affinity and specificity for the cardiac glycoside ouabain were raised in rabbits. The antigen used was a conjugate of ouabain linked through its rhamnose moiety to terminal alpha-amino groups of poly D,L alanyl-human serum albumin. Ouabain-specific antibodies were present as early as 3 wk, and rose steadily in titer over the initial 20-33 wk of immunization. Levels as high as 6.5 mg specific immunoglobulin per ml antiserum were reached in one rabbit at the end of 45 wk. The average intrinsic association constants for ouabain were 1.3 x 10(9) M(-1) and 1.6 x 10(9) M(-1) in antisera studied in detail, and there was evidence of restricted heterogeneity of binding site affinities. A high degree of specificity was demonstrated. Significant cross-reactivity occurred only with other cardioactive steroid compounds such as acetyl strophanthidin, digoxin, and digitoxin, while endogenous steroids did not cross-react even when present in 1000-fold excess. A rapid and convenient radioimmunoassay procedure for plasma or urine ouabain concentrations was developed using these antibodies. Competition between ouabain-(3)H tracer and unlabeled ouabain for specific antibody binding sites allowed the measurement of ouabain concentrations as low as 0.1 ng/ml or less without need for extraction procedures. The high association constants observed in these studies permit antibody reversal of established myocardial effects of ouabain. Both blockade and reversal of ouabain inhibition of canine myocardial microsomal Na(+), K(+)-activated ATPase by antibody were documented, suggesting a possible mechanism for reversal of cellular effects.     

Optimal conditions for measurement of Na+,K+-ATPase activity of human leucocytes

The Na+,K+-ATPase activity of human leucocytes was assayed by measuring the release of inorganic phosphate (Pi) from ATP. The maximum enzyme activity was achieved under the following conditions: concentration (mmol/l), Tris/HCl 50, Na 100, K 15, ATP 5, Mg 7, EDTA 1; pH 7.2 and temperature 37 degrees C, were optimal. Ouabain showed maximal inhibition at a concentration of 10-100 mumol/l. Ethanol, the solvent for ouabain, had a dose-related inhibitory effect. Heparin or citrate used as an anticoagulant gave similar results. Leucocyte samples could be stored at -20 degrees C for up to 6 days without loss of activity. Hypotonic lysis had advantages over sonication as the technique for cell disruption. The leucocyte Na+,K+-ATPase enzyme activity in healthy subjects was 186 mumol of Pi h-1g-1 of protein (median) with a range 136-243 mumol of Pi h-1g-1 of protein. The within-batch coefficient of variation was 6.4% and the between-batch precision was 9.6%.     

Na+,K(+)-ATPase activity and hormones in single nephron segments from nephrotic rats.

1. In the nephrotic syndrome the kidneys retain salt and water, which leads to oedema formation. The site of this sodium retention has been localized in the cortical collecting tubule by micropuncture studies. Whether or not this phenomenon is an intrinsic renal problem or is the consequence of changes in hormonal activities is still a matter of discussion. 2. Using the model of puromycin aminonucleoside-induced nephrotic syndrome in the rat, we measured Na+,K(+)-ATPase activity in nephron segments from control and nephrotic rats and investigated the regulatory role of aldosterone and endogenous-ouabain-displacing factor. 3. Nephrotic animals had a twofold increase in Na+,K(+)-ATPase activity in the cortical collecting tubule only (control versus nephrotic: 1065 +/- 68 versus 2081 +/- 274 pmol h-1 mm-1, P = 0.036), which was not modified by adrenalectomy and was independent of the kidney content of endogenous ouabain-displacing factor. Na+,K(+)-ATPase activity in the cortical collecting tubule correlated with the sodium balance in both control and nephrotic rats. 4. The data are consistent with the view that sodium retention in this model of the nephrotic syndrome is a primary event, i.e. an increase in sodium transport throughout the cortical collecting tubule expressed as a twofold increase in Na+,K(+)-ATPase activity which is no longer under hormonal regulation (aldosterone and endogenous ouabain-displacing factor).     

Reduced brain Na+, K+-ATPase activity in rats with galactosamine-induced hepatic failure: relationship to encephalopathy and cerebral oedema

Previously we have shown that sera from patients with fulminant hepatic failure (FHF) will inhibit partially purified rat brain Na+, K+-ATPase and sodium efflux from human leucocytes in vitro. Similar inhibition may be involved in the pathogenesis of encephalopathy and cerebral oedema in these patients. In the present study we have attempted to establish whether the activity of brain Na+, K+-ATPase is decreased in vivo in rats with D-galactosamine induced hepatic failure using homogenates of snap-frozen brains. Na+, K+-ATPase activity was significantly reduced in the forebrain region at the stage of mild encephalopathy (43 h after injection), while at the deeper stage of coma (43-53 h after injection) enzyme activity was further reduced in the forebrain region and was also significantly reduced in the hindbrain region. Ouabain insensitive ATPase activity was not significantly altered at any time. While a significant increase in the water content (0.5%) of the hindbrain region was found 43 h after galactosamine, there was no clear correlation between the development of cerebral oedema and the reduction of Na+, K+-ATPase activity. The activity of partially purified normal rat brain Na+, K+-ATPase was 15% lower when incubated with sera from rats in the deep stage of coma compared with control sera. These data support other evidence that the reduction in brain Na+, K+-ATPase is likely to be due to toxic substance circulating in serum which have been shown to inhibit this enzyme in vitro and to cause coma when administered to normal animals.     

Race and sex differences in erythrocyte Na+, K+, and Na+-K+-adenosine triphosphatase.

Several reports indicate that erythrocytes (RBCs) from blacks and men have higher sodium concentrations than those from whites and women. One possible mechanism to explain this finding is a difference in the activity of Na+-K+-ATPase. To explore this possibility, we have studied the Na+ and K+ kinetics of RBC Na+-K+-ATPase and RBC Na+ and K+ concentrations in 37 normotensive blacks and whites, both males and females. The maximal initial reaction velocity (Vmax) values for RBC Na+-K+-ATPase were lower in blacks and men as compared with whites and women. Higher RBC Na+ levels were observed in blacks and males vs. whites and females. Significant inverse correlations were noted between the Na+-K+-ATPase activity and RBC Na+ concentrations. These findings indicate that cellular Na+ homeostasis is different in blacks and men as compared with whites and women. Since higher RBC Na+ concentrations have also been observed in patients with essential hypertension as compared with normotensive subjects, the higher intracellular Na+ concentrations in blacks and men may contribute to the greater predisposition of these groups to essential hypertension.     

洛伐他汀对高糖诱导大鼠近端肾小管上皮细胞钠钾ATP酶活性的影响

目的洛伐他汀对高糖诱导的原代大鼠近端上皮小管上皮细胞（PTEC）钠钾ATP酶（Na＋,K＋-ATPase）活性的影响。方法采用显微微分离法体外培养大鼠PTEC,进行免疫细胞免疫化学方法鉴定细胞类型。将细胞分为正常对照组[达氏改良伊格尔（DMEM）培养液]、高糖组（25mmol／L）、高糖加小剂量洛伐他汀（高糖＋0．1μmol／LLOV）,高糖加中剂量LOV（1．0μmol／L）组,高糖加大剂量LOV（10．0μmol／L）组,检测洛伐他汀对肾小管上皮细胞氧化应激水平,液闪法测定PTEC的Na＋,K＋-ATPase活性。结果高糖组Na＋,K＋-ATPase活性显著高于正常对照组,小剂量组、中剂量组明显减低,大剂量组显著性减低。结论高糖诱导的PTECNa＋,K＋-ATPase活性明显升高,洛伐他汀对高糖诱导的原代PTEC的Na＋,K＋-ATPase活性的升高有明显抑制作用。     

有氧运动对大鼠骨骼肌线粒体Na+,K+-ATP酶和Ca2+-ATP酶及线粒体肿胀的影响

背景:研究表明有氧运动可提高线粒体功能,但在不同时期的作用特点还不明确.目的:观察不同周期有氧运动对大鼠骨骼肌线粒体Na+,K+-ATP酶和Ca2+-ATP酶以及线粒体肿胀的影响.方法:将SD大鼠随机分为正常对照组,有氧运动2,4和6周组.正常对照组不进行有氧运动,其余3组则参照BedfordTG标准,采用跑台运动方式,建立有氧运动模型进行相应的运动周期锻炼.测定各组大鼠骨骼肌线粒体Na+,K+-ATP酶和Ca2+-ATP酶的活性以及线粒体肿胀程度.结果与结论:有氧运动2周组各指标与对照组比较无差异.有氧运动4和6周组线粒体Na+,K+-ATP酶、Ca2+-ATP酶活性均增高(P<0.05),线粒体肿胀程度降低(P<0.05).实验结果表明,有氧运动可保护线粒体Na+,K+-ATP酶、Ca2+-ATP酶的活性,提高线粒体功能,但需要一定的时间积累.     

新生鼠窒息后肾组织Na+、K+-ATPase、TNF-α和NO的变化

目的探讨Na+、K+-ATPase、TNF-α和NO在新生鼠窒息后肾组织的变化及意义.方法将20只7～10日龄Wistar大白鼠随机分为窒息组和对照组,每组10只.制成常压窒息模型.在窒息30 min复氧120 min时,并分别采用酶联免疫吸附法(ELISA)、单一试剂法和定磷法检测肾组织肿瘤坏死因子-α(TNF-α)、NO含量、Na+、K+-ATPase活性.结果窒息后复氧120 min时,肾组织TNF-α、NO的含量较对照组显著升高(P＜0.05),而Na+、K+-ATPase活性下降(P＜0.05),且Na+、K+-ATPase的改变与TNF-α和NO含量之间呈显著的负相关关系(r＝-0.68和-0.72,P＜0.05),TNF-α和NO含量之间呈显著的正相关关系(r＝0.64,P＜0.05).结论窒息后肾组织Na+、K+-ATPase活性下降,其机制可能与TNF-α、NO造成细胞损伤有关.     

L-cysteine supplementation prevents exercise-induced alterations in human erythrocyte membrane acetylcholinesterase and Na+,K+-ATPase activities.

BACKGROUND: L-Cysteine (L-Cys) is implicated in the reduction of free radical production. The aim of this study was to investigate whether L-Cys supplementation prevents modulation of the activities of erythrocyte membrane acetylcholinesterase (AChE), Na(+),K(+)-ATPase and Mg(2+)-ATPase induced by free radicals in basketball players during training. METHODS: Blood was obtained from 10 basketball male players before (group A) and after a game (group B) and after 1 week of L-Cys (0.5 g/24 h orally) supplementation before (group C) and after training (group D). Lactate, pyruvate and total antioxidant status (TAS) were measured using commercial kits and the enzyme activities were determined spectrophotometrically. RESULTS: Both lactate and pyruvate levels remarkably increased after exercise. In contrast, TAS levels significantly decreased in group B, increased in group C and then declined (group D), reaching those of group A. AChE activity was statistically increased post-exercise (3.98+/-0.04 Delta OD/min x mg protein) compared with pre-training (2.90+/-0.05 Delta OD/min x mg protein, p<0.01). Na(+),K(+)-ATPase activity was also higher post-exercise (1.27+/-0.05 micromol Pi/h x mg protein) than that pre-exercise (0.58+/-0.04 micromol Pi/h x mg protein, p<0.001). When the players were supplemented with L-Cys, both AChE and Na(+),K(+)-ATPase activities remained unaltered post-exercise. Mg(2+)-ATPase activities were unchanged in all groups studied. CONCLUSIONS: L-Cys supplementation may protect the enzyme activities studied against stimulation induced by free radical production during training in athletes by ameliorating their total antioxidant capacity.