Effect of extracellular volume expansion on erythrocyte sodium transport in rats.

The effects of extracellular volume expansion (EVE) on the major sodium transport systems and sodium and potassium contents in rat erythrocytes have been examined in the present study. Study has been performed in anesthetized Wistar rat weighing about 300 g. Acute extracellular volume expansion (EVE) was induced by a constant intravenous saline infusion (3% body wt, 3 hours). Rats anaesthetized and catheterized but not expanded were used as controls. Arterial blood samples from control and expanded rats were obtained at the same time, and assayed immediately. Intracellular sodium and potassium concentration and ouabain sensitive (Na(+)-K(+)-pump) and bumetanide sensitive (Na(+)-K(+)-cotransport system) outward Na+ fluxes in erythrocytes were measured. The effect of plasma on erythrocyte transport was also analyzed by measuring 86Rb uptake. Neither of two plasma cations (Na+ and K+) were modified by the EVE. Also intracellular Na+ and K+ levels remained unvariable. Total Na+ efflux was not modified by EVE, but pump-mediated Na+ efflux was smaller after than before EVE. The ouabain-inhibible Na+ efflux rate constant decreased after EVE (from 687 +/- 81 to 525 +/- 29 h-1 x 10(-3); P less than 0.05). Both Na(+)-K(+)cotransport-mediated Na+ efflux and passive permeability increased significantly after EVE. The incubation with plasma from saline-infused animals induced a significant decrease in Rb uptake rate constant, that was not observed after incubation with plasma from non-expanded rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of membrane Na(+)-K+ Atpase of the brain, liver and RBC in rats administered di(2-ethyl hexyl) phthalate (DEHP) a plasticizer used in polyvinyl chloride (PVC) blood storage bags

Significant amounts of di(2-ethylhexyl) phthalate (DEHP) leach out into blood stored in DEHP plasticized polyvinyl chloride (PVC) bags resulting in the exposure of recipients of blood transfusion to this compound. The aim of this study was to find out whether DEHP at these low levels has any effect on the activity of membrane Na(+)-K+ ATPase, since a decrease in this enzyme activity has been reported to take place in a number of disorders like neurodegenerative and psychiatric disorders, coronary artery disease and stroke, syndrome-X, tumours etc. DEHP was administered (ip) at a low dose of 750 microg/100 g body weight to rats and the activity of membrane Na(+)-K+ ATPase in liver, brain and RBC was estimated. Histopathology of brain, activity of HMG CoA reductase (a major rate limiting enzyme in the isoprenoid pathway of which digoxin, the physiological inhibitor of Na(+)-K+ ATPase is a product), intracellular concentration of Ca2+ and Mg2+ in RBC (which is altered as a result of inhibition of Na(+)-K+ ATPase) were also studied. (In the light of the observation of increase of intracellular Ca2+ load and intracellular depletion of Mg2+ when Na(+)-K+ ATPase is inhibited). Histopathology of brain revealed areas of degeneration in the rats administered DEHP. There was significant inhibition of membrane Na(+)-K+ ATPase in brain, liver and RBC. Intracellular Ca2+ increased in the RBC while intracellular Mg2+ decreased. However activity of hepatic HMG CoA reductase decreased. Activity of Na(+)-K+ ATPase and HMG CoA reductase, however returned to normal levels within 7 days of stopping administration of DEHP. The inhibition of membrane Na(+)-K+ ATPase activity by DEHP may indicate the possibility of predisposing recipients of transfusion of blood or hemodialysis to the various disorders mentioned above. However since this effect is reversed when DEHP administration is stopped, it may not be a serious problem in the case of a few transfusion; but in patients receiving repeated blood transfusion as in thalassemia patients or patients undergoing hemodialysis, possibility of this risk has to be considered. This inhibition is a direct effect of DEHP or its metabolites, since activity of HMG CoA reductase, (an enzyme which catalyses a major rate limiting step in the isoprenoid pathway by which digoxin, the physiological inhibitor of Na(+)-K+ ATPase is synthesized) showed a decrease.     

Atrial natriuretic peptide concentration and natriuretic hormone activity in plasma of patients with chronic renal failure

To elucidate further the possible role of atrial natriuretic peptide (ANP) and hypothetical natriuretic hormone (NH) in volume and BP regulation in chronic renal failure (CRF) we measured plasma ANP, digitalis-like substances (DLS) and Na+-K+-ATPase activity (using 86Rb influx into RBC) in 9 patients with CRF before and after hemodialysis. Volume expansion between consecutive dialyses led in all patients to the elevation of plasma ANP (83.4 +/- 14.2 pmol/l) reaching in some overhydrated subjects and/or patients with concomitant cardiac insufficiency concentration greater than 150 pmol/l. Reduced 86Rb influx into RBC before hemodialysis (37.7 +/- 4.9% of controls) was accompanied by higher DLS concentrations (201 +/- 32 pmol/l). Ultrafiltration during hemodialysis with ECFV reduction lowered both ANP and DLS concentrations to 28.1 +/- 9.4 pmol/l and to 151 +/- 23 pmol/l, respectively, and abolished partly the inhibition of Na+-K+-ATPase activity (64.9 +/- 7.6% of controls). These changes corresponded to the degree of ECFV alteration. Our results suggest that both natriuretic principles are activated during ECFV expansion in CRF, probably as a corrective mechanism, with a tendency to normalize when ECFV is reduced during hemodialysis.     

Inhibition of H(+)-transporting ATPase, Ca(2+)-transporting ATPase and H+/K(+)-transporting ATPase by strophanthidin.

Studies of the effect of strophanthidin on H(+)-transporting ATPase, Ca(2+)-transporting ATPase and H+/K(+)-transporting ATPase activities are reported. Inhibition observations and kinetic results suggest the existence of a common digitalis aglycone binding site located on the extracellular surface of the enzyme, which is affected competitively by the binding of potassium to H(+)-transporting ATPase, Ca(2+)-transporting ATPase, as well as H+/K(+)-transporting ATPase and Na+/K(+)-transporting ATPase. This may lead to a better understanding of the mechanism of the pharmacological action of cardiac glycosides and imply the possibility that the positive inotropic effect may result from the inhibition of both Ca(2+)-transporting ATPase and Na+/K(+)-transporting ATPase.     

Effects of cadmium and mercury on Na(+)-K+, ATPase and uptake of 3H-dopamine in rat brain synaptosomes.

Effects in vivo of cadmium (Cd), mercury (Hg) and methylmercury (CH3Hg) on Na(+)-K+ ATPase and uptake of 3H-dopamine (DA) in rat brain synaptosomes were studied. These heavy metals significantly inhibited the Na(+)-K+ ATPase activity in a dose-dependent manner. Similarly, inhibition of DA uptake by synaptosomes was also observed in rats treated with these metals. Intraperitoneal route of metal administration was found to be more effective than per os treatment. Mercuric compounds compared to Cd elicited a higher inhibition of Na(+)-K+ ATPase and DA uptake in rat brain synaptosomes.     

Increased digitalis-like activity in human cerebrospinal fluid after expansion of the extracellular fluid volume

The present study was designed to determine whether acute expansion of the extracellular fluid volume influenced the digitalis-like activity of human cerebrospinal fluid (CSF), previously described by our laboratory. Human CSF samples, drawn before and 30 minutes after the intravenous infusion of 1 liter of either saline or glucose solutions, were assayed for digitalis-like activity by inhibition of either the 86Rb+ uptake into human erythrocytes or by the activity of a purified Na+ - K+ ATPase. The CSF inhibitory activity on both systems significantly increased after the infusion of sodium solutions but did not change after the infusion of glucose. These results indicate that the digitalis-like factor of human CSF might be involved in the regulation of the extracellular fluid volume and electrolyte content and thereby in some of the physiological responses to sodium loading.     

Changes in the expression of cardiac Na+-K+ ATPase subunits in the UM-X7.1 cardiomyopathic hamster

Previous studies have shown that cardiac Na+ -K+ ATPase activity in the UM-X7.1 hamster strain is decreased at an early stage of genetic cardiomyopathy and remains depressed; however, the mechanism for this decrease is unknown. The objective of the present study was to assess whether changes in the expression of cardiac Na+-K+ ATPase subunits in control and UM-X7.1 cardiomyopathic hamsters are associated with alterations in the enzyme activity. Accordingly, we examined sarcolemmal Na+-K+ ATPase activity as well as protein content and mRNA levels for the alpha1, alpha2, alpha3 and beta1-subunit of the Na+-K+ ATPase in 250-day-old UM-X7.1 and age-matched, control Syrian hamsters; this age corresponds to the severe stage of heart failure in the UM-X7.1 hamster. Na+-K+ ATPase activity in UM-X7.1 hearts was decreased compared to controls (9.0 +/- 0.8 versus 5.6 +/- 0.8 micromol Pi/mg protein/hr). Western blot analysis revealed that the protein content of Na+-K+ ATPase alpha1- and beta1-subunits were increased to 164 +/- 27% and 146 +/- 22% in UM-X7.1 hearts respectively, whereas that of the alpha2- and alpha3-subunits were decreased to 82 +/- 5% and 69 +/- 11% of control values. The results of Northern blot analysis for mRNA levels were consistent with the protein levels; mRNA levels for the alpha1- and beta1-subunits in UM-X7.1 hearts were elevated to 165 +/- 14% and 151 +/- 10%, but the alpha2-subunit was decreased to 60 +/- 8% of the control value. We were unable to detect mRNA for the alpha3-subunit in either UM-X7. 1 or control hearts. These data suggest that the marked depression of Na+-K+ ATPase activity in UM-X7.1 cardiomyopathic hearts may be due to changes in the expression of subunits for this enzyme.     

Inhibition of Mg2+ and Na(+)-K+ ATPases in selected tissues of fish, Cyprinus carpio under fenvalerate toxicity.

The changes in the magnesium adenosine triphosphatase (Mg2+ ATPase) and sodium-potassium adenosine triphosphatase (Na(+)-K+ ATPase) in gill, brain, liver and muscle tissues of freshwater fish, Cyprinus carpio at 6, 12, 24 and 48 hr exposure periods were studied after subjecting to sublethal concentration (10 micrograms/lit) of fenvalerate. Mg2+ ATPase and Na(+)-K+ ATPase activities were inhibited in all the tissues of fenvalerate exposed fish. The per cent inhibition increased with increase in the period of exposure and the possible reasons for the inhibition patterns are discussed.     

Vasoactive humoral systems and sodium transport in erythrocytes of normotensive offsprings of essential hypertensive subjects

Urinary excretion of sodium, potassium and some hormones influencing their transport was investigated before and after i.v. furosemide administration in 10 offsprings of normotensive subjects who had a normal Na(+)-K+ cotransport activity and in 26 normotensive men with a positive family history of essential hypertension. The latter group was divided into two subgroups with regard to the activity of red cell Na(+)-K+ cotransport. The Co[-] subjects with a decreased Na(+)-K+ cotransport activity had lower urinary excretion of sodium and vasodilators (kallikrein, dopamine, PGE2 and prostacyclin) after furosemide administration. The urinary excretion of vasopressor factors (PGF2 alpha, thromboxane) was unchanged as compared with that in the control group. There was a significant correlation between Na(+)-K+ cotransport activity and kallikrein excretion. These results suggest a deficit in the secretion of renal substances with vasodilating or natriuretic effects in Co[-] subjects. This could negatively affect their sodium excretion.     

Circulating digitalis-like substance is increased in DOCA-salt hypertension

Blood pressure and digitalis-like substance were measured in the plasma of control, salt-treated, and DOCA-salt treated rats. Blood pressure in DOCA-salt treated rats was significantly higher than that of either control or salt-treated animals. Digitalis-like activity was measured by two methods, radioimmunoassay for digoxin, and a receptor binding assay employing a rat brain synaptosomal membrane fraction. Digoxin-like immunoreactivity in plasma was not detected in either control or salt-treated rats, but was detected in DOCA-salt treated rats. Receptor binding activity in salt-treated rats was slightly but significantly higher than that of control rats. In DOCA-salt treated rats, receptor binding activity was significantly higher than that of salt-treated rats. Partial purification of the digitalis-like substance in plasma was performed by gel filtration using Sephadex G-25. Two peaks containing digoxin-like immunoreactivity were observed. Receptor binding activity, as well as Na+-K+ ATPase inhibitory activity, was detected only in the second peak, in which approximately 70% of the digoxin-like immunoreactivity was eluted. These results indicate that a circulating digitalis-like substance is increased in DOCA-salt hypertension.     

Patulin-induced ion flux in cultured renal cells and reversal by dithiothreitol and glutathione: a scanning electron microscopy (SEM) X-ray microanalysis study

Patulin (PAT), a compound produced by certain species of Aspergillus, Penicillium, and Byssochlamys, is frequently found associated with agricultural commodities. PAT has many effects on membrane function, including the inhibition of the isolated Na+-K+ ATPase. In this study, a scanning electron microscope equipped with an energy dispersive spectroscopy X-ray microanalysis system was used to examine individual cultured renal epithelial cells (LLC-PK1) in order to determine the effects of PAT on the relative intracellular ion concentrations. The estimated EC50 (60 min) for both sodium influx and potassium efflux was between 10 and 50 microns for ouabain. For PAT, the EC50 (60 min) was 250 microns for sodium influx and 100 microns for potassium efflux. However, 1 mM patulin at 240 min caused complete reversal of the sodium and potassium content of cells, and 1 mM ouabain at 240 min did not. The effect of patulin on sodium and potassium flux was both concentration and time dependent and was reversed by dithiothreitol and glutathione. PAT (250 microM) but not ouabain (250 microM) induced massive blebbing of LLC-PK1 cells. Thus, the interaction of PAT with cellular membranes involves both alterations in the regulation of intracellular ion content and the cytoskeleton. We hypothesize that patulin alters intracellular ion content via Na+-K+ ATPase and non-Na+-K+ ATPase mechanisms.     

Ischemia-reperfusion alters gene expression of Na+-K+ ATPase isoforms in rat heart

The present study investigated whether oxidative stress plays a role in ischemia-reperfusion-induced changes in cardiac gene expression of Na(+)-K(+) ATPase isoforms. The levels of mRNA for Na(+)-K(+) ATPase isoforms were assessed in the isolated rat heart subjected to global ischemia (30 min) followed by reperfusion (60 min) in the presence or absence of superoxide dismutase (5 x 10(4)U/L) plus catalase (7.5 x 10(4)U/L), an antioxidant mixture. The levels of mRNA for the alpha(2), alpha(3), and beta(1) isoforms of Na(+)-K(+) ATPase were significantly reduced in the ischemia-reperfusion hearts, unlike the alpha(1) isoform. Pretreatment with superoxide dismutase+catalase preserved the ischemia-reperfusion-induced changes in alpha(2), alpha(3), and beta(1) isoform mRNA levels of the Na(+)-K(+) ATPase, whereas the alpha(1) mRNA levels were unaffected. In order to test if oxidative stress produced effects similar to those seen with ischemia-reperfusion, hearts were perfused with an oxidant, H(2)O(2) (300 microM), or a free radical generator, xanthine (2mM) plus xanthine oxidase (0.03 U/ml) for 20 min. Perfusion of hearts with H(2)O(2) or xanthine/xanthine oxidase depressed the alpha(2), alpha(3), and beta(1) isoform mRNA levels of the Na(+)-K(+) ATPase, but had lesser effects on alpha(1) mRNA levels. These results indicate that Na(+)-K(+) ATPase isoform gene expression is altered differentially in the ischemia-reperfusion hearts and that antioxidant treatment appears to attenuate these changes. It is suggested that alterations in Na(+)-K(+) ATPase isoform gene expression by ischemia-reperfusion may be mediated by oxidative stress.     

Renal Na+-K+-ATPase in weanling and adult spontaneously hypertensive rats

The interrelationships among plasma renin activity (PRA, ng AI/ml plasma/hr), aldosterone concentration (ng%), and renal Na+-K+-ATPase activity (mumole PO4/mg protein/hr) were studied in 9 weanling normotensive spontaneously hypertensive rats (SHR), 9 adult hypertensive SHR, and 9 weanling and 9 adult normotensive Wistar-Kyoto rats (WKY). All groups were placed on a normal (0.4% sodium) diet. PRA and plasma aldosterone, measured in samples drawn from the ether-anesthetized rat, were higher in weanling SHR (15.2 +/- 2.0, 37 +/- 4.2) than in WKY. PRA measured in samples collected from a separate group of unanesthetized weanling SHR was also greater than in age-matched WKY. In adult SHR, PRA (6.1 +/- 0.9) and plasma aldosterone (20.0 +/- 2.7) were decreased. During the weanling period Na+-K+-ATPase activity in SHR was not only greater than in age-matched WKY but was also increased compared to adult normotensive and hypertensive rats (137 +/- 9 weanling SHR, 89 +/- 7 weanling WKY, 73 +/- 11 adult SHR, 84 +/- 17 adult WKY). Thus, during the weanling period the renin-angiotensin-aldosterone (R-A-A) system and renal Na+-K+-ATPase activity are activated in SHR. The elevation of Na+-K+-ATPase activity may be due to increased aldosterone levels. It was noted, however, that plasma aldosterone was similar in adult WKY and weanling SHR, while Na+-K+-ATPase activity was higher in SHR. These findings involving R-A-A and renal Na+-K+-ATPase activity prior to the elevation of blood pressure suggest that the kidneys may play a role in the initiation of hypertension in SHR.     

Altered Na+-K+ ATPase immunoreactivity within GABAergic neurons in the gerbil hippocampal complex induced by spontaneous seizure and vigabatrin treatment

In the present study, the expression of Na(+)-K(+) ATPase in the gerbil hippocampus associated with various sequelae of spontaneous seizures were investigated in order to identify the roles of Na(+)-K(+) ATPase in the epileptogenesis and the recovery mechanisms in these animals. The population of Na(+)-K(+) ATPase immunoreactive neurons and Na(+)-K(+) ATPase immunodensity were significantly lower in the pre-seizure group of SS gerbils than those in SR gerbils. At 30-min postictal, the Na(+)-K(+) ATPase immunoreactivity was significantly elevated in the hippocampal complex. At 3-h postictal, the Na(+)-K(+) ATPase immunoreactivity in the hippocampus was declined, as compared to the 30-min postictal. At 12h after seizure on-set, Na(+)-K(+) ATPase expression was re-enhanced in the all regions of the hippocampal complex including the dentate hilus. Following administration of vigabatrin Na(+)-K(+) ATPase expression was also increased. The present data suggest that altered Na(+)-K(+) ATPase expression may contribute the regulation of the seizure activity in this animal.     

HPLC method for measuring (Na(+)-K(+)) ATPase and (Ca(++)-Mg(++)) ATPase in erythrocytes from different species of mammals]

(Na(+)-K+)ATPase and (Ca(++)-Mg++)ATPase are enzymes located in erythrocyte plasma membranes, driving back ions against the electrochemical gradient; (Na(+)-K+)ATPase transports 3 Na+ ions out of the cell, and 2 K+ ions into it for each hydrolyzed ATP molecule, whereas the Ca(2+)-pump transports Ca2+ ions out of the cells, by utilizing still the ATP hydrolysis. The method used to test the activity of the above mentioned enzymes is based on the measuring of the ADP quantity released during the reaction by HPLC, that is High Performance Liquid Chromatography; the chromatographic type is a Ion-Pair Reversed-Phase. This method presents the following important advantages for the assay of the enzymes we analysed: 1) It is reproducible through time; 2) It is perfectly linear; 3) It is extremely sensitive. This method allowed us to carry out a comparative study of (Na(+)-K+)ATPase and (Ca(++)-Mg++)ATPase in erythrocyte plasma membranes of several species of mammalia: man, horse, rabbit, lamb, rat. We recovered different values in ATPase activity; (Ca(++)-Mg++)ATPase shows a higher activity than Na(+)-K+)ATPase; moreover, some differences exist in the various Mammalia considered, with relation to each pump: the lamb shows the lowest activity for both pumps, whereas the rabbit shows the highest one. At present, the different values obtained are being interpreted and analysed. This method is also very versatile, since it allowed us to assess the Km value for Ca++ of the (Ca(++)-Mg++)ATPase in erythrocyte plasma membranes of rabbit. The value resulted to be 100 microMs, thus 10 times higher than the human Km value for the Ca++.     

Differing significance of Na(+)-Ca2+ exchange in the regulation of cytosolic Ca2+ in rat exocrine gland acini and cardiac myocytes.

In order to compare the importance of Na(+)-Ca2+ exchange in the regulation of cytosolic Ca2+ concentration (Ca2+i), acini obtained from rat pancreas and submandibular glands as well as cardiac myocytes were loaded with Na+ by inhibition of Na(+)-K+ ATPase activity then loaded with fura-2. In the exocrine tissues, incubation in K(+)-free buffer or with ouabain had no substantial effect on resting Ca2+i or on the changes in Ca2+i following exposure to carbachol as compared with acini incubated under control conditions. In contrast, rat cardiac myocytes, treated identically, showed marked changes in Ca2+i under resting and stimulated conditions as compared with controls. We conclude that the Na(+)-Ca2+ exchange systems of rat pancreatic and submandibular gland acini contribute little to the overall regulation of Ca2+i at rest during cholinergic stimulation.     

An endogenous digitalis-like compound extracted from human urine: biochemical and chemical studies

Plasma and urine levels of an endogenous digitalis-like compound (EDLC) are increased in low renin Na+-dependent experimental hypertension, in some normotensive offspring of hypertensive patients and in some essential hypertensive patients. Urine-drived EDLC was purified from 550 L of urine from essential hypertensive patients (n = 8) and from normotensive subjects with a family history of hypertension (n = 27), using flash chromatography on C18 reversed-phase, anion exchange chromatography and various reversed-phase high performance liquid chromatographies. The mechanism of Na+-K+ ATPase inhibition and the related effects of semipurified urine-derived EDLC were studied and compared with those of ouabain. Its action was similar to that of ouabain in 8 out of 10 of the tests applied. The main effects of such a compound were the depression of Na+-K+ pump activity of human erythrocytes, the inhibition of 5-hydroxytryptamine reuptake by human platelets, and the induction of natriuresis in urethanized rats. Therefore, EDLC may be considered as one of the natriuretic hormones whose mechanism of action closely resembles that of ouabain.     

Estradiol-induced expression of N(+)-K(+)-ATPase catalytic isoforms in rat arteries: gender differences in activity mediated by nitric oxide donors

We tested the hypothesis that previously demonstrated gender differences in ACh-induced vascular relaxation could involve diverse Na(+)-K(+)-ATPase functions. We determined Na(+)-K(+)-ATPase by measuring arterial ouabain-sensitive 86Rb uptake in response to ACh. We found a significant increase of Na+ pump activity only in aortic rings from female rats (control 206 +/- 11 vs. 367 +/- 29 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.01). Ovariectomy eliminated sex differences in Na(+)-K(+)-ATPase function, and chronic in vivo hormone replacement with 17beta-estradiol restored the ACh effect on Na(+)-K(+)-ATPase. Because ACh acts by enhancing production of NO, we examined whether the NO donor sodium nitroprusside (SNP) mimics the action of ACh on Na(+)-K(+)-ATPase activity. SNP increased ouabain-sensitive 86Rb uptake in denuded female arteries (control 123 +/- 7 vs. 197 +/- 12 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.05). Methylene blue (an inhibitor of guanylate cyclase) and KT-5823 (a cGMP-dependent kinase inhibitor) blocked the stimulatory action of SNP. Exposure of female thoracic aorta to the Na+/K+ pump inhibitor ouabain significantly decreased SNP-induced and ACh-mediated relaxation of aortic rings. At the molecular level, Western blot analysis of arterial tissue revealed significant gender differences in the relative abundance of catalytic isoforms of Na(+)-K(+)-ATPase. Female-derived aortas exhibited a greater proportion of alpha2-isoform (44%) compared with male-derived aortas. Furthermore, estradiol upregulated the expression of alpha2 mRNA in male arterial explants. Our results demonstrate that enhancement of ACh-induced relaxation observed in female rats may be in part explained by 1) NO-dependent increased Na(+)-K(+)-ATPase activity in female vascular tissue and 2) greater abundance of Na(+)-K(+)-ATPase alpha2-isoform in females.     

Erythrocyte cation transport in arterial hypertension: interrelation with the renin-angiotensin-aldosterone system and the atrial natriuretic factor

Red cell membrane Na(+)-K+ transport systems, renin-angiotensin-aldosterone system (RAAS) and atrial natriuretic factor (ANF) were studied in a group of 50 mild essential hypertensive patients (n = 25 for each group) age, sex and blood pressure matched. Na(+)-K+ ATPase and intracellular Na+ (Na+ i) were significantly different between the two groups (p less than 0.01). A slight difference was also seen for the Na(+)-K+ cotransport (p less than 0.05) as a likely consequence of the differences in the methodology of Na+ charge to study its efflux from the red cells in vitro. A negative correlation (r = -0.47, p less than 0.01) was observed between ANF and Na(+)-K+ cotransport suggesting an interrelationship of the two systems in the homeostasis in body fluid and electrolytes.     

Cigarette smoking impairs Na+-K+-ATPase activity in the human coronary microcirculation

The extracellular K(+) concentration ([K(+)](o)) has been proposed to link cardiac metabolism with coronary perfusion and arrhythmogenesis, particularly during ischemia. Several animal studies have also supported K(+) as an EDHF that activates Na(+)-K(+)-ATPase and/or inwardly rectifying K(+) (K(ir)) channels. Therefore, we examined the vascular reactivity of human coronary arterioles (HCAs) to small elevations in [K(+)](o), the influence of risk factors for coronary disease, and the role of K(+) as an EDHF. Changes in the internal diameter of HCAs were recorded with videomicroscopy. Most vessels dilated to increases in [K(+)](o) with a maximal dilation of 55 ± 6% primarily at 12.5-20.0 mM KCl (n = 38, average: 16 ± 1 mM). Ouabain, a Na(+)-K(+)-ATPase inhibitor, alone reduced the dilation, and the addition of Ba(2+), a K(ir) channel blocker, abolished the remaining dilation, whereas neither endothelial denudation nor Ba(2+) alone reduced the dilation. Multivariate analysis revealed that cigarette smoking was the only risk factor associated with impaired dilation to K(+). Ouabain significantly reduced the vasodilation in HCAs from subjects without cigarette smoking but not in those with smoking. Cigarette smoking downregulated the expression of the Na(+)-K(+)-ATPase catalytic α(1)-subunit but not Kir2.1 in the vessels. Ouabain abolished the dilation in endothelium-denuded vessels to a same extent to that with the combination of ouabain and Ba(2+) in endothelium-intact vessels, whereas neither ouabain nor ouabain plus Ba(2+) reduced EDHF-mediated dilations to bradykinin and ADP. A rise in [K(+)](o) dilates HCAs primarily via the activation of Na(+)-K(+)-ATPase in vascular smooth muscle cells with a considerable contribution of K(ir) channels in the endothelium, indicating that [K(+)](o) may modify coronary microvascular resistance in humans. Na(+)-K(+)-ATPase activity is impaired in subjects who smoke, possibly contributing to dysregulation of the coronary microcirculation, excess ischemia, and arrhythmogenesis in those subjects. K(+) does not likely serve as an EDHF in the human coronary arteriolar dilation to bradykinin and ADP.