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PubMed1987

Monoclonal antibodies to human erythrocyte membrane Ca++-Mg++ adenosine triphosphatase pump recognize an epitope in the basolateral membrane of human kidney distal tubule cells.

Human calcium transporting tissues were examined to determine whether they contained a protein similar to the Ca++-Mg++ adenosine triphosphatase (Ca++-Mg++ATPase) pump of the human erythrocyte membrane. Tissues were processed for immunoperoxidase staining using monoclonal antibodies against purified Ca++-Mg++ATPase. In human kidneys, specific staining was found only along the basolateral membrane of the distal convoluted tubules. Glomeruli and other segments of the nephron did not stain. Staining of erythrocytes in human spleen was readily observed. Human small intestine, human parathyroid, and human liver showed no antigens that crossreacted with the antibodies to Ca++-Mg++ATPase. Specific staining of distal tubule basolateral membranes from the kidney of a chimpanzee was also noted. Our experiments show, for the first time, that basolateral membranes of the human distal convoluted tubule contain a protein that is immunologically similar to the human erythrocyte Ca++-Mg++ATPase. These observations suggest that the cells of the distal convoluted tubules of human kidney may have a calcium pump similar to that of human erythrocyte membranes.

Animals↗
PubMed1992

The role of endogenous Na+, K(+)-adenosine triphosphatase inhibitory factor in the regulation of membrane fluidity of erythrocytes in essential hypertension.

OBJECTIVE: To investigate the regulatory mechanisms of membrane functions in hypertension, we examined the relationship between endogenous Na+, K(+)-adenosine triphosphatase (ATPase) inhibitor (digitalis-like factor; DLF) and erythrocyte membrane fluidity in essential hypertension by means of an electron spin resonance (ESR) and spin labelling methods. DESIGN AND METHODS: Erythrocytes were obtained from patients with essential hypertension and normotensive subjects, and the ESR spectra for a fatty acid spin label agent (5-nitroxide stearate) incorporated into the erythrocyte membranes were studied. The DLF content in plasma was expressed as the inhibitory potency of dog kidney Na+, K(+)-ATPase activity in vitro. RESULTS: The values of outer hyperfine splitting and of order parameter in ESR spectra were significantly higher in hypertensive patients than in normotensive subjects. This finding shows that the erythrocyte membrane fluidity may be decreased in essential hypertension. The level of plasma DLF content was greater in hypertensive patients than in normotensive subjects and was significantly correlated with the decrease in erythrocyte membrane fluidity. CONCLUSIONS: These results suggest that the decrease in erythrocyte membrane fluidity may be partially dependent upon the increased plasma DLF content.

Blood Proteins↗
PubMed1987

Catalytic properties of the F1-adenosine triphosphatase from Escherichia coli K-12 and its genetic variants as revealed by 18O exchanges.

We have examined intermediate Pi-water oxygen exchange during [gamma-18O]ATP hydrolysis by the F1 adenosine triphosphatase from Escherichia coli K-12. Water oxygen incorporation into each Pi released was increased as ATP concentration was lowered as observed previously for the same reaction catalyzed by the enzyme from eukaryotic sources. Heterogeneous distributions of 18O in product Pi were produced by coexisting epsilon subunit-replete and epsilon subunit-depleted enzyme molecules. The epsilon-replete enzyme showed a much higher probability for oxygen exchange. These data imply that the epsilon subunit inhibits net ATP hydrolysis by imposing conformational constraints which reduce the cooperative conformational interactions that promote ADP and Pi release. Four enzyme variants altered in alpha or beta subunit structure with reduced net hydrolytic activity showed sharply increased oxygen exchange during ATP hydrolysis. Heterogeneity was apparent in the 18O distribution of the product Pi, however. That behavior could reflect hindered conformational interactions and/or increased affinity of the alpha 3 beta 3 gamma delta complex for the epsilon subunit. In contrast, enzyme from mutant uncA401 showed very little oxygen exchange accompanying hydrolysis of 20 microM ATP. This is the only enzyme so far reported with this unusual property. Its rate limitation appears to be in the hydrolytic rather than the product release step of the catalytic sequence.

Animals↗
PubMed1995

Turnover of the gastric H+,K(+)-adenosine triphosphatase alpha subunit and its effect on inhibition of rat gastric acid secretion.

BACKGROUND & AIMS: The rate of turnover and the effect of inhibition of acid secretion on the turnover of gastric H+,K(+)-adenosine triphosphatase (ATPase) is unknown. The aim of this study was to determine the turnover of the alpha subunit of gastric H+,K(+)-ATPase in rats under control conditions and during inhibition of acid secretion by ranitidine or omeprazole. METHODS: The turnover of the alpha subunit of the ATPase was determined by measuring the loss of incorporated 35S-methionine. This was compared with the rate of recovery of K(+)-stimulated ATPase activity in the omeprazole-treated animals. RESULTS: The half-life of the alpha subunit was 54 hours. A 1-week treatment with omeprazole had no significant effect, but the half-life increased to 125 hours (P < 0.01) after continuous ranitidine infusion. After omeprazole treatment, K(+)-stimulated ATPase activity recovered with a half-time of 15 hours. CONCLUSIONS: The turnover of the gastric ATPase subunit was independent of omeprazole inhibition but was prolonged by ranitidine. The effect of ranitidine suggests that the resting pump in tubulovesicles may turn over more slowly than the stimulated pump in the secretory canaliculus. The rapid recovery of ATPase activity compared with turnover after omeprazole is caused by both H+,K(+)-ATPase synthesis and loss of covalently bound drug.

Animals↗
PubMed1994

Cation transport mediated by Na+,K(+)-adenosine triphosphatase in lymphoblastoma cells from patients with bipolar I disorder, their relatives, and unrelated control subjects.

In an investigation of cation transport in bipolar affective disorder, we have measured parameters related to Na+,K(+)-adenosine triphosphatase, the enzyme that carries out active transport of sodium and potassium, in lymphoblastoid cells cultured from patients with bipolar affective disorder, age-matched nonaffected family relatives, and unrelated control subjects. Patients had lower ion transport per cell and per transport enzyme site than did related or unrelated control subjects. The rate of transport per cell appeared higher in nonaffected relatives of patients than in unrelated control subjects, though this difference did not reach significance. These data suggest that abnormally regulated ion transport may be associated with bipolar affective disorder independently of clinical state.

Biological Transport, Active↗
PubMed1982

The effect of lithium chloride on renal structure and sodium-potassium-adenosine triphosphatase activity in dogs.

Lithium chloride was given intraperitoneally to dogs at a dosage of 125 mg/kg body weight for three days. Kidneys were removed for morphologic examination and quantitation of sodium-potassium-adenosine triphosphatase (Na-K-ATPase) activities in cortical and medullary tissue. Light microscopy showed no changes in the kidneys, but cytoplasmic vacuolation and dilatation of the cisternae of the endoplasmic reticulum were seen ultrastructurally in the epithelial cells of the distal tubule and cortical and medullary collecting ducts. Mean cortical Na-K-ATPase activity was 1.49 +/- 0.25 and 1.70 +/- 0.31 mumoles inorganic phosphate/mg protein/hour in control and experimental groups respectively. Mean medullary Na-K-ATPase activity was 4.71 +/- 0.41 and 5.01 +/- 0.47 mumoles inorganic phosphate/mg protein/hour in control and experimental groups respectively. It was concluded that lithium produced morphologic changes in the distal nephron, but had no effect on renal Na-K-ATPase activity.

Aldosterone↗
PubMed1997

Transcription of the rat sarcoplasmic reticulum Ca2+ adenosine triphosphatase gene is increased by 3,5,3'-triiodothyronine receptor isoform-specific interactions with the myocyte-specific enhancer factor-2a.

Thyroid hormone (T3) increases the transcription of the sarcoplasmic reticulum Ca2+ adenosine triphosphatase (ATPase) gene (SERCA 2) through three thyroid hormone response elements. The existence of repetitive cis elements with different configurations is likely to serve specific functions such as interactions with nuclear transcription factors. In addition, the presence of different T3 receptor isoforms (T3Rs) may contribute to another level of complexity in providing specificity for T3 action. In this study, we investigated T3R alpha 1-vs. T3R beta 1-specific interactions with the myocyte enhancer-specific factor-2 (MEF-2) on the expression of the SERCA 2 gene in transient transfection assays in embryonal heart-derived H9c2 cells. MEF-2a in combination with either T3R alpha 1 or T3R beta 1 isoforms resulted in a 2.5-fold increase in SERCA 2 transgene expression in the absence of T3. Addition of T3 did not induce any further increase in SERCA 2 expression when T3R alpha 1 and MEF-2a expression vectors were cotransfected. In contrast, in the presence of T3R beta 1 and MEF-2, the addition of T3 increased chlorampenicol acetyltransferase activity by an additional 2.2-fold to a total 5.5-fold increase. The interaction between MEF-2a and T3R is transcription factor specific because another factor that binds to MEF-2 consensus sites (heart factor 1b) was not able to interact with T3R. In addition, MEF-2a failed to interact with other nuclear factors (cAMP response element-binding protein and Egr-1) that stimulate SERCA 2 gene transcription. In addition, we found that a single homologous thyroid hormone response element is not able to mediate the interactions between MEF-2a and T3Rs to increase SERCA 2 gene transcription. Our findings point to T3R isoform-specific interactions with a cell type-specific transcription factor (MEF-2) in the regulation of SERCA 2 gene expression.

Animals↗
PubMed1991

[The effects of crude drugs using diuretic on horse kidney (Na+ + K+)-adenosine triphosphatase].

In the folk-medicine, several kinds of crude drugs are used as diuretics. Twenty three kinds of diuretic drugs were chosen, and examined for their effects on the horse kidney (Na+ + K+)-adenosine triphosphatase (ATPase), which is an intrinsic enzyme of the plasma membrane and responsible for the active transport of Na+ and K+ across the membrane. Twenty one out of twenty three kinds of ethanol extracts of diuretic drugs inhibited the kidney (Na+ + K+)-ATPase activity. The intensity of the inhibition of these drugs was compared by estimating the amounts of their ethanol extracts which inhibited the (Na+ + K+)-ATPase activity by 50% (I50, micrograms/ml). Among these drugs, Atractylodis Lanceae Rhizoma (I50 = 12.8) Atractylodis Rhizoma (I50 = 15.2), Plantaginis Semen (I50 = 16.0), Plantaginis Herba (I50 = 16.0) and Alismatis Rhizoma (I50 = 22.0), have strong inhibitory effects on the kidney (Na+ + K+)-ATPase activity. The ethanol extracts of the rhizomes of Atractylodes lancea De Candolle and Atractylodis japonica Kitamura were examined with varying concentrations of ATP and ouabain. The mode of inhibition of these two extracts on the (Na+ + K+)-ATPase activity appeared to be uncompetitive with respect to ATP as judged from Lineweaver-Burk plot. The ethanol extract of Atractylodes japonica Kitamura decreased the I50 for ouabain from 1.6 x 10(-7) to 7.0 x 10(-9) M, while that of Atractylodes lancea De Candolle did not change the I50 for ouabain.

Animals↗
PubMed1988

Effects of milrinone on Ca++-sensitivity of myofibrillar Mg-adenosine triphosphatase isolated from normal human and canine hearts.

Sensitization or desensitization of cardiac actomyosin to calcium has been demonstrated with several pharmacological agents. The effect of milrinone on the sensitivity of cardiac Mg-adenosine triphosphatase (ATPase) activity to calcium was studied in purified myofibrils isolated from normal human hearts (after accidental death or trauma that caused no cardiac damage as established by the attending physician) and from normal canine hearts (established by echocardiography), over a range of calcium concentrations (pCa, 8 to 5). Caffeine, a cardiac stimulant that has been shown to increase the sensitivity of myofibrillar Mg-ATPase activity to calcium in rat ventricle, was used in this study to establish its effect on canine and human myofibrils in comparison with that of milrinone. Caffeine, at concentrations of 40 mM, caused statistically significant sensitization of canine and human myofibrils to calcium. In canine myofibrils, the calcium-dependent Mg-ATPase activity increased from 11.0 +/- 1.2 to 18.8 +/- 2.6 nmol of Pi per mg of protein per min at pCa 6.73 (N = 9, P less than .05) and from 32.9 +/- 2.1 to 37.3 +/- 2.2 nmol of Pi per mg of protein per min at pCa 6.16 (N = 9, P less than .05), whereas total Mg-ATPase activity increased from 23.4 +/- 1.5 to 33.6 +/- 2.6 nmol of Pi per mg of protein per min at pCa 6.73 (N = 9, P less than .05) and from 45.2 +/- 2.2 to 52.2 +/- 2.5 nmol of Pi per mg of protein per min at pCa 6.16 (N = 9, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗