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PubMed1974

Interactions of a photo-affinity ATP analog with cation-stimulated adenosine triphosphatases of human red cell membranes.

To identify and isolate ATP binding and hydrolyzing sites of human red cell membranes we have synthesized a photo-activated ATP analog, 8-azido adenosine triphosphate (N(3)ATP). In the absence of ultraviolet light it is a substrate for both the Mg-ATPase and the ouabain-sensitive, Na,K-ATPase. Hydrolysis of N(3)ATP is prevented by increasing concentrations of ATP. Photolysis of N(3)ATP with red cell membranes results in covalent incorporation and irreversible inhibition of both ATPase activities. Also, only three protein components of the red cell membranes are labeled. This labeling is completely abolished by appropriate concentrations of ATP.

Adenosine Triphosphatases↗
PubMed1989

H+/K+-adenosine triphosphatase inhibitors. A new approach to the treatment of acid-peptic diseases.

Due to its potent and long-lasting antisecretory properties is omeprazole, the first clinically used H+/K+-adenosine triphosphatase inhibitor, highly effective in healing of duodenal and gastric ulcers and reflux oesophagitis. Omeprazole is superior to all other presently available antiulcer drugs in the treatment of Zollinger-Ellison syndrome and refractory ulcers. Short-term administration of the drug is safe. However, serum gastrin and gastric enterochromaffin-like cells should be carefully monitored during long-term treatment with the drug.

Duodenal Ulcer↗
PubMed1998

The effect of glucose and calcium on Ca2+-adenosine triphosphatase in pancreatic islets isolated from a normal and a non-insulin-dependent diabetes mellitus rat model.

Regulation of calcium balance is important in the secretory function of pancreatic islets. Ca2+-adenosine triphosphatase (ATPase) is altered in tissues of non-insulin-dependent diabetes mellitus (NIDDM) rats, and they have an impaired response to glucose, "glucose blindness." We propose that the glucose blindness of the diabetic islet is the result of defective cellular calcium metabolism. Since Ca2+-ATPase activity is important in the regulation of calcium balance, we investigated the effect of glucose and/or calcium on Ca2+-ATPase activity in pancreatic islets in vitro and compared it with the effect in freshly isolated islets from controls and from rats with NIDDM induced by streptozotocin neonatally. Islets were isolated using collagenase and were stored fresh or cultured up to 2 days in RPMI 1640 in the presence of different concentrations of glucose and calcium. Membrane Ca2+-ATPase activity, insulin secretion, and insulin content were determined. Ca2+-ATPase activity was 1.30 +/- 0.20 micromol/L Pi/microg membrane protein in normal noncultured islets and 1.02 +/- 0.15 in islets cultured in 5.6 mmol/L glucose. Ca2+-ATPase activity progressively decreased to 0.56 +/- 0.10 and 0.34 +/- 0.14 micromol/L Pi/microg membrane protein when glucose was increased in the culture media to 16.6 and 27.7 mmol/L, respectively. Decreasing glucose to 2.8 mmol/L did not alter Ca2+-ATPase activity. Increasing or decreasing the Ca2+ content of the media did not significantly change Ca2+-ATPase activity. Islets isolated from NIDDM rats had lower basal Ca2+-ATPase activity and insulin content compared with normal controls. Incubation of islets from diabetic rats in high glucose further decreased the Ca2+-ATPase content, but incubation in low glucose did not reverse it. Insulin secretion was responsive to glucose and calcium in normal islets, but was suppressed in islets from diabetic animals. From these studies, we conclude that high glucose, but not calcium, decreases Ca2+-ATPase activity in islets from normal rats. Islets from NIDDM rats with glucose blindness have decreased Ca2+-ATPase activity, likely due to the glucose status. We suggest that this decreased Ca2+-ATPase activity may contribute to the pancreatic islets' glucose blindness.

Animals↗
PubMed1967

The effect of tropomyosin on the adenosine triphosphatase activity of desensitized actomyosin.

1. Tropomyosin preparations of the Bailey type, and those prepared in the presence of dithiothreitol to prevent oxidation of protein thiol groups, inhibit the Ca(2+)-activated adenosine triphosphatase (ATPase) of desensitized actomyosin by up to 60%. 2. The inhibitory activity of myofibrillar extracts and tropomyosin survives various agents known to denature proteins but to the action of which tropomyosin is unusually stable, namely heating at 100 degrees and mild tryptic digestion. It is destroyed by prolonged treatment with trypsin. 3. The ethylenedioxybis-(ethyleneamino)tetra-acetic acid (EGTA)-sensitizing factor present in extracts of natural actomyosin and myofibrils could be selectively destroyed, leaving unchanged the inhibitory effect on the Ca(2+)-activated ATPase. There was no correlation between the EGTA-sensitizing and the Ca(2+)-activated inhibitory activities of tropomyosin prepared under different conditions. 4. Optimum inhibition was achieved when tropomyosin and the myosin of desensitized actomyosin were present in approximately equimolar proportions. Tropomyosin had no effect on the Ca(2+)-activated ATPase of myosin measured under similar conditions. 5. Evidence is presented showing that the tropomyosin binds to desensitized actomyosin under the conditions in which the ATPase is inhibited.

Journal Article↗
PubMed1987

Triiodothyronine-induced cyst formation in metanephric organ culture: the role of increased Na-K-adenosine triphosphatase activity.

Previous organ culture investigations into the pathogenesis of renal cyst formation have demonstrated that glucocorticoid-induced proximal tubular cyst formation is associated with increases in renal sodium-potassium adenosine triphosphatase (Na-K-ATPase) activity. To explore the relationship between cyst production and transport enzyme induction, we examined the effects of the potent inducer of Na-K-ATPase activity, L-3,5,3'-triiodothyronine (T3), on renal tubular morphologic and enzymatic development in murine metanephric organ culture. The addition of T3 (2 X 10(-8) mol/L) to completely characterized, serum-free growth medium produced striking proximal tubular cystic abnormalities. Frank cyst development was preceded by ultrastructural alterations consisting of basolateral intercellular spreading, which increased with progressive tubular dilation. Ultrastructural analysis demonstrated no abnormalities of tubular cyst wall basal laminae, and immunohistologic staining with affinity-purified antibodies to the basal lamina glycoproteins fibronectin, laminin, and entactin, revealed no differences between cystic and control tissue. With use of an enzyme-linked kinetic microassay, T3-induced cystic organ culture explants (CY) showed significant increases in Na-K-ATPase when compared with controls from 72 to 120 hours of organ culture incubation. The initial differences in CY Na-K-ATPase occurred contemporaneously with the earliest ultrastructural evidence of cyst formation, and subsequent increases paralleled progressive tubular cyst formation. Tubular cyst formation in CY could be largely prevented by daily incubation of explants with ouabain, 0.2 mmol/L (final concentration) for 120 minutes without deleterious effects on overall metanephric development. We conclude that T3 induces proximal tubular cyst formation in metanephric organ culture, and that T3-induced increases in Na-K-ATPase have a primary role in the pathogenesis of tubular cyst formation in this model system.

Animals↗
PubMed1995

Inositol phosphates modulate human red blood cell Ca(2+)-adenosine triphosphatase activity in vitro by a guanine nucleotide regulatory protein.

D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] inhibits human red blood cell (RBC) Ca(2+)-stimulable, Mg(2+)-dependent adenosine triphosphatase (Ca(2+)-ATPase) activity in vitro. Because we have previously shown that adrenergic receptors exist on the human mature RBC membrane and can modulate Ca(2+)-ATPase activity, we examined the possibility that a guanine nucleotide regulatory protein (G protein) mediated the Ins(1,4,5)P3 effect. Guanosine 5'-O-(3-thiotrisphosphate) (GTP gamma S) 10(-4) mol/L also inhibited RBC Ca(2+)-ATPase activity. Pertussis toxin 200 ng/mL blocked the effects of both Ins(1,4,5)P3 and GTP gamma S on Ca(2+)-ATPase activity. In separate studies, pertussis toxin-catalyzed adenosine diphosphate (ADP) ribosylation was shown to occur in RBC membranes under conditions in which measurements of Ca(2+)-ATPase activity were performed. When Ins(1,4,5)P3 10(-7) mol/L and GTP gamma S 10(-6) mol/L were added to membranes concurrently, their inhibitory actions on the enzyme were additive. At greater concentrations of Ins(1,4,5)P3 (10(-6) to 10(-5) mol/L) and GTP gamma S (10(-4) mol/L), the inositol phosphate reversed the inhibitory effect of GTP gamma S. These observations indicate that the novel effect of Ins(1,4,5)P3 on the activity of a plasma membrane Ca(2+)-ATPase depends at least in part on the action of a pertussis toxin-susceptible G protein.

Adult↗
PubMed2000

Early development of human gastric H,K-adenosine triphosphatase.

BACKGROUND: Little is known about the early development of the gastric acid secretion in human neonates. The purpose of this study was to examine the early development of gastric H,K-adenosine triphosphatase (ATPase) by analyzing human gastric biopsy specimens. METHODS: Eighty-eight neonates from week 25 to week 42 of gestation who were treated in a neonatal intensive care unit underwent gastroscopy with biopsy specimens obtained from the corpus. The expression of gastric H,K-ATPase protein in the gastric biopsy specimens was assessed by Western blot analysis, using an antibody directed against the gastric H,K-ATPase. The amount of H,K-ATPase expressed was compared with age, gender, clinical factors, diseases, and the macroscopic and histologic findings at endoscopy. RESULTS: The expression of human gastric H,K-ATPase increased significantly with gestational age. There was a significant increase in the expression of gastric H,K-ATPase during the first 82 days after birth. Boys had a significantly higher expression of gastric H,K-ATPase than girls did, when it was adjusted for gestational and postnatal age. Neither the clinical features nor treatments showed significant correlations with the expression of human gastric H,K-ATPase when controlling for gestational and postnatal age. CONCLUSIONS: This study shows that human gastric H,K-ATPase is expressed from week 25 of gestation, which agrees with earlier findings of gastric pH in preterm infants. The amount of enzyme expressed increases with gestational and postnatal age. The authors speculate that the susceptibility to gastric lesions seen in neonates is not related to the amount of H,K-ATPase. However, studies elucidating the ontogeny of gastric mucosal defense mechanisms are warranted.

Biopsy↗
PubMed2002

Transient hypoxia-ischemia in rats: changes in diffusion-sensitive MR imaging findings, extracellular space, and Na+-K+ -adenosine triphosphatase and cytochrome oxidase activity.

PURPOSE: To investigate the correlation between diffusion-weighted (DW) magnetic resonance (MR) image changes with alterations in extracellular volume and changes in cytochrome oxidase and Na(+)-K(+)-adenosine triphosphatase (ATPase) activity at various times during and after cerebral hypoxia-ischemia in neonatal and juvenile rats. MATERIALS AND METHODS: One- and 4-week-old rats were randomly assigned to control or transient cerebral hypoxia-ischemia (ie, right carotid artery occlusion plus exposure to 8% oxygen) groups. Hypoxic-ischemic changes compared with normal ipsilateral brain tissue on DW images and the apparent diffusion coefficient of water were measured during and at 1 and 24 hours after hypoxia-ischemia ended. Hypoxic-ischemic changes in extracellular space and ipsilateral versus contralateral differences in Na(+)-K(+)-ATPase and cytochrome oxidase activity were measured. RESULTS: Hyperintensities on DW images obtained during hypoxia-ischemia correlated well (P <.05) with extracellular space reductions, which occurred 15 minutes earlier in the brains of 4-week-old rats than in the brains of 1-week-old rats. Similarly, within 1 hour after hypoxia-ischemia ended, DW image and extracellular space changes normalized. In contrast, Na(+)-K(+)-ATPase and cytochrome oxidase activity decreased in some regions during hypoxia-ischemia and remained reduced 1 hour after the end of hypoxia-ischemia. Twenty-four hours after signal intensity normalization, hyperintense areas reappeared on DW images, and Na(+)-K(+)-ATPase and cytochrome oxidase activity remained decreased. CONCLUSION: Signal intensity alterations with diffusion-sensitive MR imaging during and after transient hypoxia-ischemia are closely associated with a corresponding shrinkage and reexpansion of the extracellular space, irrespective of age. Mechanisms other than Na(+)-K(+)-ATPase changes may induce the early cell volume changes detected with diffusion-sensitive MR imaging.

Animals↗