Autoradiographic and cytochemical localization of (Na+-K+)-activated adenosine triphosphatase in the acini of dog salivary gland (author's transl)

The distribution of Na pump sites (Na+-K+ ATPase) in the acinar cells of dog submandibular gland was demonstrated by light and electron microscopical radioautography of 3H-ouabain binding sites and electron microscopical ATPase cytochemistry. The grains of 3H-ouabain by light microscopical radioautography were localized to the basal parts of acini and/or the striated ducts, and a small quantity of the grains was also present on the luminal parts of acini. The grains of 3H-ouabain by electron microscopical radioautography and the reaction products of ATPase were found to be localized on the basolateral plasma membrane of both serous and mucous cells, while slightly on the microvilli of the luminal plasma membranes. The present evidence that the distribution of ATPase on the acinar cells determined by the cytochemistry is well concomitant with that of 3H-ouabain binding sites on the acinar cells by the radioautography, suggests that the above mentioned ATPase is Na+-K+ ATPase, a Na pump. The relationship of the distribution of the Na+-K+ ATPase and the cation transport of the plasma membranes in the acinar cells of the dog submandibular gland are discussed.     

Erythrocyte sodium content, sodium transport, ouabain binding capacity and Na+, K+-ATPase activity in lean and obese subjects

Erythrocyte sodium content, sodium transport (ouabain-sensitive efflux rate of sodium, and ouabain-sensitive efflux rate constant of sodium) 3H ouabain binding capacity and sodium-potassium-activated ouabain-sensitive adenosine triphosphatase (Na+-K+-ATPase) activity were measured in 18 lean subjects and 25 obese subjects. The mean erythrocyte sodium content, sodium transport and ouabain binding capacity of obese subjects were the same as in lean subjects. There was no relationship between obesity index (wt/ht2) and sodium transport. We conclude that erythrocyte sodium transport in most obese patients is normal.     

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++.     

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.     

Seasonal changes in glycogen content and Na+-K+-ATPase activity in the brain of crucian carp

Changes in the number of Na+-K+-ATPase alpha-subunits, Na+-K+-ATPase activity and glycogen content of the crucian carp (Carassius carassius) brain were examined to elucidate relative roles of energy demand and supply in adaptation to seasonal anoxia. Fish were collected monthly around the year from the wild for immediate laboratory assays. Equilibrium dissociation constant and Hill coefficient of [3H]ouabain binding to brain homogenates were 12.87+/-2.86 nM and -1.18+/-0.07 in June and 11.93+/-2.81 nM and -1.17+/-0.06 in February (P>0.05), respectively, suggesting little changes in Na+-K+-ATPase alpha-subunit composition of the brain between summer and winter. The number of [3H]ouabain binding sites and Na-K-ATPase activity varied seasonally (P<0.001) but did not show clear connection to seasonal changes in oxygen content of the fish habitat. Six weeks' exposure of fish to anoxia in the laboratory did not affect Na+-K+-ATPase activity (P>0.05) confirming the anoxia resistance of the carp brain Na pump. Although anoxia did not suppress the Na pump, direct Q10 effect on Na+-K+-ATPase at low temperatures resulted in 10 times lower catalytic activity in winter than in summer. Brain glycogen content showed clear seasonal cycling with the peak value of 203.7+/-16.1 microM/g in February and a 15 times lower minimum (12.9+/-1.2) in July. In winter glycogen stores are 15 times larger and ATP requirements of Na+-K+-ATPase at least 10 times less than in summer. Accordingly, brain glycogen stores are sufficient to fuel brain function for about 8 min in summer and 16 h in winter, meaning about 150-fold extension of brain anoxia tolerance by seasonal changes in energy supply-demand ratio.     

Biochemical characterization of plasma membrane isolated from human skeletal muscle

Specific components of ion translocation systems were studied in excitable plasma membranes isolated from normal human muscle. Na+-K+ ATPase and ouabain-sensitive K+ phosphatase activities were 8.9 +/- 1 mumol Pi/h per mg protein and 96 +/- 9 nmol/min per mg protein, respectively. Scatchard analysis of equilibrium binding assays with [3H]ouabain showed non-linear curves consistent with high- and low-affinity sites (estimated Kd 3 nM and 0.22 microM). Two families of receptors with different affinities for a tritiated TTX derivative (estimated Kd 0.4 and 4 nM) were also identified suggesting the existence in human muscle of at least two classes of voltage-dependent Na+ channels. In addition (+)-[methyl-3H]PN200-110, a potent Ca2+ antagonist used for labeling voltage-dependent Ca2+ channels, was observed to bind to a homogeneous population of receptors in the plasma membrane (Kd = 0.2 nM).     

Association of androgen binding sites with the endoplasmic reticulum of rat ventral prostate

Microsomes from ventral prostate of 24-h castrated rats contain a single set of tissue-specific high-affinity, low-capacity androgen binding sites. These sites are indigenous to the endoplasmic reticulum, as shown by purification procedures associated with marker enzymes and electron microscopic analyses. When prostatic microsomal membranes are separated from plasma membranes using the nuclear or the mitochondrial pellets as the source of fractionation in sucrose gradients, the androgen binding activity is selectively associated with fractions rich in rough endoplasmic reticulum and ribosomes. Eighty-four percent of the total content of Na+/K+ adenosine triphosphatase (ATPase) and only 27% of the total binding capacity were concentrated in fractions rich in smooth-surfaced vesicular membranes, when nuclear suspensions constituted the membrane source. In contrast, the region of the same gradient when enriched in rough endoplasmic reticulum and deficient in plasma membrane content contained 73% of the androgen-binding capacity and only 14% of the ATPase. For fractions collected using mitochondrial suspensions as starting material, the ratio (total glucose-6-phosphatase/total binding capacity) was closer to 1.0 than similar ratios of ATPase/binding capacity, indicating co-sedimentation of binding sites with microsomal membranes and not with plasma membranes. Na+/K+ ATPase, but not 5' nucleotidase, is a valid plasma membrane marker for ventral prostate. Microsomal androgen receptors may constitute a new level of regulation of androgen action in target cells.     

Erythrocyte ouabain binding and intracellular Na+ in normotensive obese women and obese women receiving medication for hypertension

People with "primary obesity" may be hypertensive because they have lost their ability to compensate for the effect of low Na+-K+-ATPase levels on blood pressure. In obese patients receiving hypertensive medication (n = 13), but not in normotensive nonmedicated patients (n = 42), diastolic blood pressure was inversely correlated with erythrocyte ouabain binding (P less than 0.02) and directly correlated with intracellular Na+ concentration (P less than 0.01). Moreover, there was a stronger inverse relationship between ouabain binding and intracellular Na+ in patients receiving medication for hypertension (P less than 0.01) than in normotensive patients (P less than 0.05). These data suggest that patients receiving hypertensive medication may be less able to compensate than normotensive patients, (a) for the potential effect of Na+-K+-ATPase levels on intracellular Na+ and (b) for the potential effect of intracellular Na+ concentration on diastolic blood pressure. We propose that obese people with low levels of ouabain binding (primary obesity) may have an increased risk of developing hypertension if their compensatory mechanisms fail.     

Method for the preparation of human erythrocyte membrane with low basal calcium ATPase, responsive to stimulation

A simple procedure for preparing erythrocyte membranes with low basal Ca2+ ATPase activity is described, which is stimulated several-fold by the addition of hemolysate in the incubation mixture. The cells are hemolyzed in hypotonic imidazole buffer and resulting membranes are washed with hypotonic phosphate buffer (pH 8.0) and the hemolyzing medium. The membrane preparations also have Mg2+-stimulated and Na+-K+-stimulated ATPase activities. The method allows the comparison of basal Ca2+ ATPase as well as hemolysate- or calmodulin-stimulated Ca2+ ATPase activities and thus may be useful in studying Ca2+ ATPase activity in various physiopathological conditions.     

Prolonged exercise to fatigue in humans impairs skeletal muscle Na+-K+-ATPase activity, sarcoplasmic reticulum Ca2+ release, and Ca2+ uptake.

Prolonged exhaustive submaximal exercise in humans induces marked metabolic changes, but little is known about effects on muscle Na+-K+-ATPase activity and sarcoplasmic reticulum Ca2+ regulation. We therefore investigated whether these processes were impaired during cycling exercise at 74.3 +/- 1.2% maximal O2 uptake (mean +/- SE) continued until fatigue in eight healthy subjects (maximal O2 uptake of 3.93 +/- 0.69 l/min). A vastus lateralis muscle biopsy was taken at rest, at 10 and 45 min of exercise, and at fatigue. Muscle was analyzed for in vitro Na+-K+-ATPase activity [maximal K+-stimulated 3-O-methylfluorescein phosphatase (3-O-MFPase) activity], Na+-K+-ATPase content ([3H]ouabain binding sites), sarcoplasmic reticulum Ca2+ release rate induced by 4 chloro-m-cresol, and Ca2+ uptake rate. Cycling time to fatigue was 72.18 +/- 6.46 min. Muscle 3-O-MFPase activity (nmol.min(-1).g protein(-1)) fell from rest by 6.6 +/- 2.1% at 10 min (P <0.05), by 10.7 +/- 2.3% at 45 min (P <0.01), and by 12.6 +/- 1.6% at fatigue (P <0.01), whereas 3[H]ouabain binding site content was unchanged. Ca2+ release (mmol.min(-1).g protein(-1)) declined from rest by 10.0 +/- 3.8% at 45 min (P <0.05) and by 17.9 +/- 4.1% at fatigue (P < 0.01), whereas Ca2+ uptake rate fell from rest by 23.8 +/- 12.2% at fatigue (P=0.05). However, the decline in muscle 3-O-MFPase activity, Ca2+ uptake, and Ca2+ release were variable and not significantly correlated with time to fatigue. Thus prolonged exhaustive exercise impaired each of the maximal in vitro Na+-K+-ATPase activity, Ca2+ release, and Ca2+ uptake rates. This suggests that acutely downregulated muscle Na+, K+, and Ca2+ transport processes may be important factors in fatigue during prolonged exercise in humans.     

Green tea metabolite EGCG protects membranes against oxidative damage in vitro

Green tea polyphenols like epigallocatechin gallate (EGCG) have been proposed as a cancer chemopreventative. Several studies have shown that EGCG can act as an antioxidant by trapping proxyl radicals and inhibiting lipid peroxidation. The main propose of this study is to investigate the antioxidant capacity of EGCG using erythrocyte membrane-bound ATPases as a model. The effects of EGCG on t-butylhydroperoxide-induced lipid peroxidation and the activity of membrane-bound ATPases in human erythrocyte membranes were studied. The extent of oxidative damage in membranes was assessed by measuring lipid peroxidation, (TBARS, thiobarbituric acid reactive substances formation) and the activity of ATPases (Na(+)/K(+), Ca(2+), and CaM-activated Ca(2+) pump ATPases). EGCG blocked t-BHP induced lipid peroxidation in erythrocyte membranes, significantly (0.45 +/- 0.02 vs 0.20 +/- 0.01; t-BHP vs t-BHP + EGCG respectively, microm/L TBARS) (p < 0.05). EGCG also protected ATPases against t-BHP induced damage; for Na/K ATPase (2.4 +/- 0.2 vs 1.6 +/- 0.1 vs 2.44 +/- 0.2, nmol Pi/min/mg protein, control vs t-BHP vs t-BHP and EGCG respectively), for Ca ATPase (5.8 +/- 0.4 vs 3.9 +/- 0.3 vs 5.6 +/- 0.34, nmol Pi/min/mg protein, control vs t-BHP vs t-BHP and EGCG respectively) and for CaM-Ca ATPase (14.7 +/- 0.7 vs 7.3 +/- 0.4 vs 11.6 +/- 0.55, nmol Pi/min/mg protein, control vs t-BHP vs t-BHP and EGCG respectively) (p < 0.05). In conclusion our results indicate that EGCG is a powerful antioxidant that is capable protecting erythrocyte membrane-bound ATPases against oxidative stress.     

Effects of steroid hormones on total brain Na(+)-k+ ATPase activity in Oreochromis mossambicus

The effects of administration of cortisol, corticosterone, testosterone, progesterone and a synthetic estrogen. diethylstilbestrol (DES) on total brain Na(+)-K+- ATPase were investigated in tilapia, O. mossambicus. Exogenous administration of 0.125 and 0.25 microg/g body weight of glucocorticoids and 0.125, 0.25 and 0.5 microg/g body weight of DES for 5 days significantly stimulated Na+(-) K+ ATPase activity by 14-41% in the brain, while 0.5 microg/g body weight of glucocorticoids did not evoke any response on the activity of the enzyme. Progesterone (0.125 and 0.25 microg/g body weight) administration significantly decreased the enzyme activity by 21-36% and high dose (0.5 microg/g body weight) was ineffective. Testosterone exhibited a biphasic effect on Na(+)-K+ ATPase activity--a low dose stimulated by 14% while middle and high doses inhibited it by 19-24%. The results seem to be the first report on the effect of steroids on brain ATPase activity in a teleost. When 0.25microg/g body weight of actinomycin D or puromycin was administered prior to the treatment of similar doses of hormones, the inhibitors significantly inhibited the effect of the hormones by 24-52%. This clearly shows that the effect of the hormones was sensitive to the action of inhibitors suggesting a possible genomic mode of action under long-term treatment. The results suggest that cortisol, corticosterone and DES may possibly stimulate the co-transport of glucose and excitation of membrane potential while progesterone and testosterone inhibit them in the brain of O. mossambicus by regulating the activity of Na(+)-K+ ATPase.     

Purification and molecular properties of the (sodium + potassium)-adenosinetriphosphatase and reconstitution of coupled sodium and potassium transport in phospholipid vesicles containing purified enzyme.

Recent work in our laboratory on the purification and characterization of the (sodium + potassium)-activated adenosinetriphosphatase (NaK ATPase) has been reviewed. Two enzymes have been purified, that from the rectal salt gland of the spiny dogfish, Squalus acanthias and that from the electric organ of the electric eel, Electrophorus electricus. The enzyme appears to consist of two catalytic subunits of molecular weight of about 95,000 and one glycoprotein with a molecular weight of about 50,000. The amino acid composition, N-terminal amino acids, and the carbohydrate composition of these subunits have been determined. The phospholipid composition of the holoenzyme has also been determined. The protein component shows very little variation with evolution, but the carbohydrate and phospholipid components show considerable variation. It has been possible to form vesicles from the purified enzyme from Squalus acanthias and to demonstrate the ATP-dependent, ouabain inhibitable, coupled uphill transports of Na+ and K+. The properties of these transports are very similar to those observed previously in intact erythrocytes or resealed erythrocyte ghosts with respect to asymmetries of binding sites, stoichiometries of Na+ and K+ transported, Na+-Na+ exchange, and K+-K+ exchange. It is concluded that the NaK ATPase is the molecular machine for effecting Na+ and K+ transport in the intact cell membrane.     

Thallium inhibition of ouabain-sensitive sodium transport and of the (Na+ plus K+)-ATPase in human erythrocytes.

The influence of Tl+ on Na+ transport and on the ATPase activity in human erythrocytes was studied. 0.1-1.0 mM Tl+ added to a K+-free medium inhibited the ouabain-sensitive self-exchange of Na+ and activated both the ouabain-sensitive 22Na outward transport and the transport related ATPase. 5-10mM external Tl+ caused inhibition of the ouabain-sensitive 22Na efflux as well as the (Na+ plus Tl+)-ATPase. Competition between the internal Na+ and rapidly penetrating thallous ions at the inner Na+-specific binding sites of the erythrocyte membrane could account for the inhibitory effect of Tl+. An increase of the internal Na+ concentration in erythrocytes or in ghosts protected the system against the inhibitory effect of high concentration of Tl+. A protective effect of Na+ was also demonstrated on the (Na+ plus Tl+)-ATPase of fragmented erythrocyte membranes studied at various Na+ and Tl+ concentrations.     

K+ transport in resting rat hind-limb skeletal muscle in response to paraxanthine, a caffeine metabolite

This study tested the hypothesis that paraxanthine, a caffeine metabolite, stimulates skeletal muscle potassium (K+) transport by an increase in Na+ -K+ ATPase activity. The unidirectional transport of K+ into muscle (J(in)K) was studied using a perfused rat hind limb technique. Using 12 hind limbs, we examined the response to 20 min of paraxanthine perfusion (0.1 mM), followed by 20 min perfusion with 0.1 mM paraxanthine and 5 mM ouabain (n = 5) to irreversibly inhibit Na+ -K+ ATPase activity. Paraxanthine stimulated J(in)K by 23+/-5% within 20 min. Ouabain abolished the paraxanthine-induced stimulation of J(in)K, suggesting the increase in K+ uptake was due to activation of the Na+ -K+ ATPase. To confirm the role of the Na+ -K+ ATPase, 14 hind limbs were perfused for 20 min with 5 mM ouabain prior to 20 min perfusion with 0.1 mM paraxanthine and 5 mM ouabain (n = 6). Ouabain alone resulted in a 41+/-7% decrease in J(in)K within 15 min. Inhibition of ouabain-sensitive J(in)K prevented the paraxanthine-induced increase in J(in)K. Hind limbs (n = 3) were also perfused with 0.1 mM paraxanthine for 60 min to examine the response to longer duration paraxanthine perfusion. The paraxanthine-induced increase in J(in)K continued for the entire 60 min. In another series, hind limbs were perfused with 0.01 (n = 9), 0.1 (n = 9), or 0.5 (n = 6) mM paraxanthine for 15 min. There was no concentration-dependent relationship between J(in)K and paraxanthine concentration, and 0.01, 0.1, and 0.5 mM paraxanthine increased J(in)K similarly (25+/-5, 22+/-4, and 27+/-6%, respectively). The effect of paraxanthine on J(in)K could not be reversed by subsequent perfusion with paraxanthine-free perfusate. Caffeine (0.05-1.0 mM) had no effect on K+ transport. It is concluded that paraxanthine increases J(in)K in resting skeletal muscle by stimulating ouabain-sensitive Na+ -K+ ATPase activity.     

Class I antiarrhythmic drug effects on ouabain binding to guinea pig cardiac Na+ -K+ ATPase

The notion that the inhibition of the Mg2+ -dependent ATP-hydrolytic function of the myocardial Na+ -K+ ATPase by class I antiarrhythmic agents occurs as a result of their binding to the same receptor sites as the digitalis glycosides was tested by performing competitive binding assays of [3H]ouabain (OUA) with eight drugs: disopyramide, encainide, lidocaine, lorcainide, phenytoin, procainamide, quinidine, and tocainide in guinea pig heart microsomal preparations. In the first set of experiments, 10-200 microM concentrations of the drugs were preincubated with the enzyme and displacement assays performed with 250 nM OUA. The drugs showed receptor occupancy of 19-32% at 50 microM, 25-44% at 100 microM, and 37-56% at 200 microM. Then, 10-500 nM concentrations of OUA were preincubated with the enzyme, and competitive assays were performed using 200 microM concentrations of the drugs. OUA occupied 39-51% of the receptor sites at 100 nM, 44-67% at 250 nM, and 62-82% at 500 nM, displacing the drugs in a concentration-dependent fashion. The results show that antiarrhythmic drugs interact with the same or similar receptor sites as ouabain on the Na+ -K+ ATPase, pointing to a possible contribution of these interactions to the mechanism for their inhibitory actions on the enzyme, and perhaps their arrhythmogenic effects.     

Effects of sulfhydryl compounds on the inhibition of erythrocyte membrane Na+(-)K+ ATPase by ozone

Exposure of human erythrocyte membranes to ozone (5 mumol/10 min) resulted in the inhibition of erythrocyte membrane Na+(-)K+ ATPase (EC.3.6.1.39). It was determined that, the degree of enzyme inhibition in the directly ozone exposed membranes was greater than that of membranes obtained from ozone exposed intact erythrocytes. In the presence of varying concentrations (0-1.0 mM) of dithiotrethiol or mercaptoethanol Na+(-)K+ ATPase activities of both types of ozone exposed membranes were increased almost proportionally with the concentration of dithiotrethiol or mercaptoethanol however, the activities were still lower than the normal Na+(-)K+ ATPase value. The results indicate that, dithiotrethiol or mercaptoethanol prevent the enzyme inhibition by ozone in vitro. This suggests that the membrane thiol groups are primary targets for ozone and thereby preventing the oxidation of essential functional groups of enzyme protein.     

竹红菌甲素对红细胞膜上几种酶光敏失活作用的研究

Hypocrellin A (HA)-sensitized photoinactivation of enzymes in human erythrocyte membrane, including AchE, GPDH, Na(+)-K+ ATPase, Ca2(+)-Mg2+ ATPase were studied in this paper. The sensitivity of these four enzymes inactivated by HA and light are as following order: Ca2(+)-Mg2+ ATPase greater than Na(+)-K+ ATPase greater than GPDH greater than AchE. The relationship among ATPase inactivation, sulfhydryl photoinactivation and lipid peroxidation was also investigated. Results show that SH group photooxidation probably is one of the major reasons of enzyme inactivation whereas lipid peroxidation has little effect. The isolated GPDH was less sensitive than that membrane-bound, GSH, NAD acted protectively on GPDH and ATPase respectively. The evidence of electrophoresis and protein intrinsic fluorescence showed that protein structure did not change significantly even though most activity had lost in case of GPDH.     

Erythrocyte Na+-ATPase in obese patients

Na+-K+-ATPase activity, as measured by erythrocytic 86Rb uptake and number Digoxin Binding Sites were evaluated in 34 obese patients and in 39 control subjects. No differences were found in 86Rb uptake and Digoxin Binding Sites between obese and controls. Likewise no differences were found between obese patients on their spontaneous caloric intake and those studied during various hypocaloric regimens. Finally, no relationship between thyroid hormone serum concentrations and ATPase activity was found in the group of obese patients.     

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.