Reversal of one-kidney, one-clip hypertension in rats. Effects on myocardial Na+, K(+)-ATPase, arterial Na(+)-K+ pump, arterial membrane potential, and plasma Na(+)-K+ pump inhibitory activity.

We have previously reported that myocardial microsomal Na+,K(+)-ATPase activity, arterial wall ouabain-sensitive 86Rb uptake, and arterial smooth muscle cell membrane potentials are decreased and plasma Na(+)-K+ pump inhibitory activity is increased in rats during the fifth week of one-kidney, one-clip hypertension. We here report measurements of these four parameters and blood pressure following unclipping. A new series of rats with one-kidney, one-clip hypertension was prepared. Each animal was paired with a one-kidney, sham-clipped (nonconstricting clip) control rat. After 5 weeks, the clips were removed. In the hypertensive animals arterial pressure promptly (within 3 h) returned to normal and remained at the level for 7 observation days. On the third day following unclipping, all four parameters were not significantly different from those in the paired control animals. On the seventh day following unclipping, three of the four parameters were not significantly different from those in the paired control animals and arterial ouabain sensitive 86Rb uptake was slightly increased relative to the value in the control animals. These studies invite further inquiry into the possible role of plasma Na(+)-K+ pump inhibitory activity in the genesis and maintenance of the hypertension in this model.

Effects of canrenone on blood pressure in rats with reduced renal mass.

Canrenone, a metabolic product of spironolactone, which competes with ouabain for binding to Na-K-ATPase at the digitalis receptor site and by itself inhibits Na-K-ATPase, was administered intramuscularly to reduced renal mass-saline drinking hypertensive and reduced renal mass-distilled water drinking normotensive rats for 8 days. Reduced renal mass-saline hypertension in the rat, is a low renin, volume expanded form of hypertension. Rats with this type of hypertension have been shown to have depressed arterial Na-K pump activity and increased Na-K pump inhibitory activity in their plasma. Canrenone treatment caused a progressive decrease in blood pressure in the hypertensive rats and this was associated with normalization of Na-K pump activity in arteries. Water and salt intake and excretion did not change. On the other hand, canrenone progressively increased blood pressure in the normotensive rats and this was associated with positive inotropy in isolated papillary muscles. These findings suggest that the depressed pump activity and the pump inhibitor play a role in reduced renal mass-saline hypertension in the rat and that the rise in blood pressure in the normotensive rats probably reflects canrenone's ability, by itself, to inhibit Na-K-ATPase.

Inhibition of alpha-aminoisobutyric acid uptake by mastoparan in Madin-Darby Canine Kidney cells.

Mastoparan, a wasp venom, was found to inhibit Na(+)-dependent net alpha-aminoisobutyric acid (AIB) uptake in Madin Darby Canine Kidney (MDCK) cells. Mastoparan also produced a significant increase in AIB efflux when compared to controls. Pretreatment of MDCK cells with 2 mM neomycin attenuated mastoparan's inhibition of net AIB uptake and completely suppressed mastoparan-mediated increases in AIB efflux when compared to controls. These data suggest that mastoparan's inhibition of net AIB uptake involves more than a single basic mechanism.

Mastoparan inhibits rat renal NaK-ATPase activity.

Rat renal NaK-ATPase was inhibited by mastoparan in a dose dependent fashion. This inhibition reached completion within 30 seconds. Due to mastoparan's rapid effects on NaK-ATPase activity, this inhibition does not appear to involve either a decrease in the rate of synthesis or an increase in their degradation of NaK-ATPase since these processes require a latency period of at least several minutes. In addition, the phosphoenzyme intermediate formed in the presence of mastoparan was greater than that formed in its absence further indicating that inhibition of NaK-ATPase by mastoparan is not due to a decrease in the number of NaK-ATPase. A possible mechanism for the inhibition is that mastoparan stabilizes the phosphoenzyme intermediate and reduces the Vmax of the enzyme by decreasing the rate of turnover of existing enzyme sites. Neomycin, an inhibitor of inositol phospholipid metabolism, was also found to attenuate the inhibition of Na,K-ATPase by mastoparan, suggesting that the mechanism of this inhibition may involve degradation of the phosphatidylinositol "pool".

Pathophysiological role of cation transport and natriuretic factors in hypertension.

This review considers in some detail the hypothetical relationships between sodium fluxes, both active and passive, across the cell membrane, and intracellular sodium concentration in vascular smooth muscle in the animal models of hypertension. It appears that two basic types of transport defects, increased cell membrane permeability to sodium and decreased active pumping of sodium at a given internal sodium concentration, can exist in vascular smooth muscle in experimental hypertension, and that sometimes the two defects coexist, further increasing internal sodium concentration. It is possible that eventually we may find similar transport defects in vascular smooth muscle in humans with arterial hypertension. Decreased active pumping at a given internal sodium concentration appears to result from a humoral sodium pump inhibitor. Future directions for research in the area are also considered. First priority should be given efforts to determine the chemical structure of the sodium pump inhibitor(s). High priority should also be given to attempts to measure passive and active sodium fluxes and intracellular sodium concentration in vascular smooth muscle cells in vivo, and to determine the role of atrial natriuretic factor in the genesis and maintenance of hypertension.

Decreased myocardial Na+K+ATPase activity in rats with reduced renal mass-saline hypertension.

Inhibition of cardiovascular Na,K-pump activity has been shown to promote an increase in the contractile activity of myocardial and vascular smooth muscle and a consequent rise in blood pressure (BP). It has also been shown that vascular Na,K-pump activity and myocardial Na+K+ATPase activity [the energy source for active sodium (Na) and potassium (K) transport] are decreased in rats with various forms of low renin hypertension including rats with reduced renal mass-saline (RRM-saline) hypertension. In the present study, left ventricular Na+K+ATPase activity from rats with RRM-saline hypertension was found to be decreased in membranes prepared by two independent methods: deoxycholate, sodium iodide (Nal)-treated microsomal fractions (method 1) and membranes prepared by the hypotonic, lithium bromide (LiBr) method (method 2). Relative to RRM normotensive control rats which drank distilled water, myocardial Na+K+ATPase activity from RRM-saline drinking rats was decreased by 18.2% in membranes prepared by method 1 and 33.6% in membranes prepared by method 2. The apparent affinities of Na+K+ATPase for K and for ouabain were unaltered relative to controls in membranes prepared from these hypertensive rats by method 1, and the sialic acid content and 5'-nucleotidase activity (two putative sarcolemmal markers) were unaltered in membranes from the hypertensive rats, prepared by methods 1 and 2 respectively. The Mg2+ATPase activity of membranes prepared by method 1 was increased in the RRM-saline hypertensive rats but because it was not increased in membranes prepared by method 2 the former observation does not appear to be of any pathophysiological importance. In other experiments, hypertension was reversed in RRM-saline hypertensive rats by restricting their salt intake (substitution of distilled water for drinking).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of rat cardiac and renal Na+,K+-ATPase by high sodium concentrations and vanadate.

In the present study, rat renal Na+,K+-ATPase was found to be more sensitive to inhibition by high Na+ concentrations (100-400 mM) than was rat cardiac Na+,K+-ATPase. K+ was more effective in reversing the inhibition by Na+, of cardiac relative to renal Na+,K+-ATPase. Rat renal Na+,K+-ATPase was also more sensitive than cardiac Na+,K+-ATPase to inhibition by vanadate over this range of Na+ concentrations. These results support the hypothesis that vanadate may selectively regulate Na+,K+-ATPase in the kidney, and they may also help explain the natriuretic and diuretic effects of vanadate in rats. Inhibition of renal Na+,K+ATPase by Na+, may also help explain, in part, the natriuretic and diuretic effects of acute saline loading.

Myocardial (Na+,K+)-ATPase activity in Dahl salt-sensitive and resistant rats.

Vascular (Na+,K+)-pump activity (ouabain-sensitive 86Rb+ uptake) and myocardial (Na+,K+)-ATPase activity are reduced in animals with various forms of low renin, experimental hypertension. On the other hand, vascular (Na+,K+)-pump activity is increased in Dahl salt-sensitive relative to resistant rats (a genetic model of hypertension), regardless of salt intake or blood pressure and it is also increased in Dahl salt-sensitive rats on high salt (8% NaCl) relative to low salt (0.4% NaCl) diets. It has been suggested that this increase in vascular (Na+,K+)-pump activity may be secondary to an increase in the vascular sarcolemmal permeability to Na+ in these salt-sensitive rats. In the present study, (Na+,K+)-ATPase activity of left ventricular microsomal fractions, was increased in Dahl salt-sensitive relative to resistant rats on low salt diets; however, this difference disappeared when these salt-sensitive and resistant rats were placed on high salt diets. In contrast, myocardial (Na+,K+)-ATPase activity was decreased in Dahl salt-sensitive rats on high relative to low salt diets. Evidence that this decrease in (Na+,K+)-ATPase activity is not secondary to myocardial hypertrophy in the hypertensive salt-sensitive rats, and mechanisms by which decreased cardiovascular (Na+,K+)-pump activity, increased sarcolemmal permeability or both, might contribute to elevated blood pressure, are discussed.

Greater sensitivity to vanadate of rat renal relative to cardiac (Na+ + K+)-ATPase.

Vanadate (VO4(-3] produces a positive inotropic effect in rats and also promotes diuresis as well as natriuresis. Although the mechanism(s) of these effects is uncertain, in the kidney, VO4(-3) may act through inhibition of (Na+ + K+)-ATPase activity, whereas in the heart, other or additional mechanisms are likely. Under the assay conditions used in the present study, microsomal (Na+ + K+)-ATPase activities from rat kidney cortex and medulla were inhibited to a greater extent than was left ventricular (Na+ + K+)-ATPase activity over a range of VO4(-3) concentrations. The apparent dissociation constant for left ventricular (Na+ + K+)-ATPase (10.95 +/- 1.26 X 10(-7)M VO4(-3] was significantly greater than that of (Na+ + K+)-ATPase from the cortex (3.46 +/- 0.96 X 10(-7)M VO4(-3] or the medulla (3.32 +/- 0.7 X 10(-7)M VO4(-3), N = 6, P less than .05) whereas there were no significant differences between the effects of VO4(-3) on (Na+ + K+)-ATPase from the cortex and medulla. The greater inhibition by VO4, of (Na+ + K+)-ATPase from the cortex relative to that of the left ventricle, occurred over a range of Na+ and K+ concentrations, and K+ enhanced the inhibition by VO4(-3) to a greater extent for (Na+ + K+)-ATPase from the cortex than the left ventricle. These results suggest that renal (Na+ + K+)-ATPase is more sensitive than left ventricular (Na+ + K+)-ATPase to inhibition by VO4(-3) and would, therefore, be more likely to be modulated in vivo.

Effects of rat atrial extract on sodium transport and blood pressure in the rat.

Atrial cardiocytes contain specific atrial granules ( SAGs ) which are the storage site of atrial natriuretic factor (ANF). The purpose of the present study was to determine whether ANF produces natriuresis by inhibiting Na+-K+ pump activity and whether this factor is similar to the humoral sodium transport inhibiting factor ( HSTIF ) previously demonstrated in acutely volume expanded animals and humans as well as in experimental and human essential hypertension. Our results indicate that, in contrast to the HSTIF , ANF does not inhibit membrane Na+,K+-ATPase, vascular smooth muscle cell Na+-K+ pump activity, or sodium transport in the toad bladder. Intravenous infusion of ANF in the bilaterally nephrectomized, hexamethonium-treated rat produces only a small transient pressor response, probably due to potentiation of endogenous norepinephrine. These findings strongly suggest that the ANF is not the same as the HSTIF detected on acute volume expansion and in some forms of hypertension. They also suggest that the diuretic and natriuretic effects of ANF are due to mechanism(s) other than blood pressure elevation and inhibition of Na+-K+ pump activity.

Myocardial Na,K-ATPase activity in rats with steroid and spontaneous hypertension.

Vascular Na-K pump activity (ouabain-sensitive 86Rb uptake) and cardiac Na,K-ATPase activity are decreased in rats with one-kidney, one clip and reduced renal mass-saline hypertension. In the present study we measured left ventricular, microsomal Na,K-ATPase activity in rats with two steroid forms of hypertension; one-kidney, deoxycorticosterone acetate-saline (1-K, DOCA-saline) and one-kidney, dexamethasone (1-K, DEXA) hypertension and also in spontaneously hypertensive rats (SHR). Relative to one-kidney, normotensive (1-K, NT) control rats, cardiac Na,K-ATPase activity was decreased and Mg-ATPase activity was increased in rats with 1-K, DOCA-saline hypertension (systolic BP = 175 +/- 2 mmHg, sustained eight to 10 weeks, n = 11). The apparent dissociation constant of cardiac Na,K-ATPase for K was unchanged in these hypertensive rats. In rats with 1-K, DEXA hypertension (systolic BP = 171 +/- 1 mmHg, sustained eight to 10 weeks, n = 9), cardiac Na,K-ATPase activity was increased and Mg-ATPase activity was unchanged relative to 1-K, NT control rats. We observed no change in either cardiac Na,K-ATPase activity or Mg-ATPase activity in SHR (36-38 weeks of age, systolic BP = 186 +/- 7 mmHg, n = 12) relative to either age-matched normotensive Wistar-Kyoto or Wistar control rats. These studies therefore suggest that cardiac Na,K-ATPase activity is decreased in 1-K, DOCA-saline hypertensive rats, increased in 1-K, DEXA hypertensive rats and unchanged in SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Red cell membrane Ca-ATPase in cystic fibrosis: increased activation by Na.

In the present study, we compared the kinetics of activation by Na, of red cell membrane Ca-ATPase of cystic fibrosis (CF) patients and healthy volunteers (controls). Calmodulin (membrane-free hemolysate) was included in the assay medium to promote maximal Ca-ATPase activation. There were no significant differences between the red cell Ca-ATpase activities of the two groups, assayed either in the absence or in the presence of optimal concentrations of Na. There were also no significant differences between the apparent dissociation constants or Hill coefficients for activation of red cell Ca-ATPase by Na. On the other hand, the percent activation by Na of red cell Ca-ATPase activity of the CF patients was approximately 40% greater than that of the controls. The additional increment of Ca-ATPase activity due to the elevated percent activation was about 14% of the total red cell Ca-ATPase activity of the CF patients. Although this increment of Ca-ATPase activity is relatively small, the increased percent activation by Na does suggest an alteration in the enzyme's response to Na. At present we do not know whether or not this alteration applies to Ca-transport or if it is of any pathophysiological importance.

Decreased myocardial Na+-K+-ATPase activity in one-kidney, one-clip hypertensive rats.

We have previously shown that Na+-K+ pump activity (ouabain-sensitive 86Rb uptake) is decreased in vascular tissue of animals with various forms of low renin hypertension. In the present study we measured Na+-K+-ATPase activity, the energy source for Na+-K+ pumping, in membrane fractions prepared from myocardial tissue of rats with chronic one-kidney, one-clip hypertension and their one-kidney normotensive controls. Membranes were prepared by two independent methods: microsomal fractions (method 1) and fractions prepared by the hypotonic LiBr method of Dhalla et al. (method 2). In membranes prepared from left ventricles of the hypertensive rats (by method 1) Na+-K+-ATPase activity was decreased, Mg2+-ATPase activity was increased, and the sialic acid content and 5'-nucleotidase activity (two putative membrane markers) were unchanged relative to the control rats. The sensitivity of cardiac Na+-K+-ATPase to inhibition by ouabain was also unchanged. Na+-K+-ATPase activity was also decreased in the right ventricles (method 1) of these hypertensive rats, suggesting that this defect is probably not pressure related. In membranes prepared from the left ventricles of the hypertensive rats by method 2, Na+-K+-ATPase activity was again reduced, whereas the Mg2+-ATPase and 5'-nucleotidase activities were unchanged relative to the controls. These studies suggest that myocardial Na+-K+-ATPase activity is suppressed in rats with this low renin form of hypertension and the possible effect of this suppression on myocardial contractile activity is discussed.

Effect of prolonged dietary administration of vanadate on blood pressure in the rat.

Vanadate, a potent naturally occurring Na+,K+-ATPase inhibitor thought to have a role in regulating Na+-K+ pump activity, was fed to uninephrectomized rats drinking tap water or a 1% solution of sodium chloride for as long as 56 weeks. Feeding was achieved by adding sodium orthovanadate to normal rat chow equivalent to 100 or 200 ppm vanadium by weight. In the rats drinking tap water, systolic pressure gradually increased over a period of several weeks and then was sustained in a dose-related manner for the duration of the treatment. The increased pressure was not associated with changes in water intake, urine output, or urinary sodium excretion but correlated positively with plasma vanadium levels ranging from 0.04 to 0.27 microgram/ml. Increased pressure was associated with increased heart-to-body-weight ratio but did not appear to occur in a small group of animals drinking the 1% solution of sodium chloride. These findings, considered in the light of others, indicate that vanadate deserves continued study in relation to hypertension.

Vascular sodium-potassium pump activity in various models of experimental hypertension.

1. Ouabain-sensitive 86Rb uptake was used to assess sodium-potassium pump activity in vascular smooth muscle of animals with various types of experimental hypertension. 2. The findings suggest that pump activity is suppressed in the non-genetic low renin, presumably volume-expanded forms of hypertension. 3. By contrast, pump suppression does not appear to be involved in spontaneously hypertensive rats or in salt-induced hypertension in Dahl's salt-sensitive rats. In these genetic models the primary defect may be increased cell membrane permeability.

Altered activity of the sodium-potassium pump in arteries of rats with steroid hypertension.

1. Ouabain-sensitive uptake of 86Rb, a measure of the Na+-K+ pump activity, was studied in tail arteries of rats made hypertensive with deoxycorticosterone and saline. 2. Decreased activity of the ouabain-sensitive Na+-K+ pump supports the hypothesis that the activity of Na+-K+ pump is suppressed in volume expanded hypertension.