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James SG, Appleby GJ, Miller KA, Steen JT, Colquhoun EQ, Clark MG. Purine and pyrimidine nucleotide metabolism of vascular smooth muscle cells in culture. GENERAL PHARMACOLOGY 1996; 27:837-44. [PMID: 8842687 DOI: 10.1016/0306-3623(95)02087-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
1. Cultures of vascular smooth muscle cells accumulate extracellular breakdown products of purine and pyrimidine nucleotides that, over 9 hr, represent 60 +/- 7 and 78 +/- 17%, respectively, of the intracellular nucleotide content. 2. The accumulation is stimulated during contracture with 20 mM KCl or 70 microM carbachol, consistent with the notion that both pyrimidine and purine nucleotides are involved in the energetics of smooth muscle contracture. 3. Because the intracellular levels of pyrimidine and purine nucleotides remain constant, it appears likely that rates of synthesis match the rates of release. 4. Ectonucleotidases are present that can degrade ATP, UTP, and CTP. High-energy nucleotides may be the primary products released.
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Affiliation(s)
- S G James
- Department of Biochemistry, University of Tasmania, Hobart, Australia
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Cheung PK, Visser J, Bakker WW. Upregulation of antithrombotic ectonucleotidases by aspirin in human endothelial cells in-vitro. J Pharm Pharmacol 1994; 46:1032-4. [PMID: 7714716 DOI: 10.1111/j.2042-7158.1994.tb03262.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Ecto ATP-diphosphohydrolase (apyrase) activity of human endothelial cells following aspirin treatment has been studied in-vitro. It was shown by HPLC analysis of supernatant samples that pre-incubation of the cultures with aspirin resulted in a significantly increased turnover of supplemented ATP into its degradation products (ADP and AMP). Enhanced expression of ectoenzyme after aspirin treatment could be observed as demonstrated by immunofluorescence-staining with monoclonal anti-apyrase antibodies. This suggests enhancement of endothelial ATP-diphosphohydrolase activity induced by aspirin. The present data obtained in human vascular cells in-vitro are in line with results from previous animal studies in-vivo, suggesting a novel cyclooxygenase-independent antithrombotic activity of aspirin.
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Affiliation(s)
- P K Cheung
- Department of Pathology, University of Groningen, The Netherlands
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Hills BA. Oesophageal surfactant: evidence for a possible mucosal barrier on oesophageal epithelium. AUSTRALIAN AND NEW ZEALAND JOURNAL OF MEDICINE 1994; 24:41-6. [PMID: 8002857 DOI: 10.1111/j.1445-5994.1994.tb04424.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
BACKGROUND There is a growing body of evidence to indicate that the gastric mucosa is protected against the back-diffusion of acid by a physical barrier comprising surface-active phospholipid (SAPL) otherwise known as gastric surfactant on account of its similarity to pulmonary surfactant in composition and behaviour. AIMS To determine whether this form of mucosal protection might extend into the oesophagus to offer some degree of protection against the reflux of gastric contents. METHODS Oesophageal epithelium was tested for the same hydrophobicity which is characteristically imparted to gastric mucosa by SAPL. A morphological study was also performed to visualise any barrier, purposely avoiding conventional fixatives for electron microscopy which destroy hydrophobic surfaces. RESULTS Oesophageal epithelium in the vicinity of the cardiac sphincter was found to be appreciably hydrophobic, although not as hydrophobic as gastric mucosa. This hydrophobicity was eliminated by bile salts selected as a known 'barrier breaker' and one which reacts with any lining of SAPL. The morphological study revealed much evidence of SAPL, especially that lining epithelial cells, while its source is probably the lamellar bodies also visualised. CONCLUSIONS These findings indicate a physical barrier of oesophageal surfactant which could offer some degree of protection against gastro-oesophageal reflux but one which is particularly prone to attack by bile.
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Affiliation(s)
- B A Hills
- Department of Physiology, University of New England, Armidale, NSW
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Côté YP, Filep JG, Battistini B, Gauvreau J, Sirois P, Beaudoin AR. Characterization of ATP-diphosphohydrolase activities in the intima and media of the bovine aorta: evidence for a regulatory role in platelet activation in vitro. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1139:133-42. [PMID: 1610912 DOI: 10.1016/0925-4439(92)90092-2] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The inner layer of the aorta contains the enzyme ATP diphosphohydrolase (ATPDase: EC 3.6.1.5) which catalyzes the sequential phosphorolysis of ATP----ADP----AMP. Two zones of the inner layer, the intima and media, were separated and both were shown to contain ATPDase activity of similar specific activity (0.08 and 0.10 U/mg protein, respectively). However, the media exhibited about 100-times more enzyme activity than the intima. Both preparations were virtually identical with respect to pH optima (7.5), migration patterns after electrophoresis under non-denaturing conditions, relative rates of ATP and ADP hydrolysis and potency to inhibit ADP-induced platelet aggregation in both human platelet-rich plasma and whole blood. The IC50 values for ADP (2 microM)-induced aggregation were 6.8 and 12.9 mU/ml in platelet-rich plasma and whole blood, respectively. Addition of ATPDase to platelets pre-aggregated with ADP resulted in a dose-dependent disaggregation in platelet-rich plasma (IC50 4.9 mU/ml), but not in whole blood. When both ATPDase (5.6-58.7 mU/ml) and ATP (0.5-10 microM) were added to platelet-rich plasma, there was an immediate dose-dependent aggregation of platelets followed by a slowly developing disaggregation. These data show that ATPDase is present in both the intima and media layers of bovine aorta and suggest a dual role for this enzyme in platelet activation. By converting ATP released from damaged cells into ADP, the enzyme could facilitate platelet aggregation at the site of vascular injury, whereas the subsequent conversion of ADP to AMP could inhibit or reverse platelet aggregation. The consequence of these activities would be to control the growth of a platelet thrombus.
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Affiliation(s)
- Y P Côté
- Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Québec, Canada
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Moodie FD, Baum H, Butterworth PJ, Peters TJ. Purification and characterisation of bovine spleen ADPase. EUROPEAN JOURNAL OF BIOCHEMISTRY 1991; 202:1209-15. [PMID: 1837267 DOI: 10.1111/j.1432-1033.1991.tb16492.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
ADPase has been purified from bovine spleen. Electrophoresis revealed a minor contaminent in the preparation that may represent ADPase that has been decreased in size by limited proteolysis during extraction and purification. The native enzyme behaves on SDS/PAGE as a 100-kDa protein but ADPase is a glycoprotein and so its electrophoretic behaviour may be anomalous. The apparent molecular mass is decreased to 70 kDa after removal of carbohydrate by treatment with a glycosidase. The use of a cross-linking reagent followed by electrophoresis suggests that the enzyme is composed of a single subunit. The specific activity of the purified material was 115 U/mg protein. The enzyme catalyses the hydrolysis of nucleoside di- and tri-phosphates but nucleoside monophosphates are not acted upon. The Km for ADP (approx. 10-15 microM) is unaffected by the state of purification of the enzyme, but catalytic activity of the purified material is stimulated by inclusion of detergent in the assay system and by calcium ions. Maximum activity is seen at pH 8.0-8.5 with ADP as substrate but the optimum shifts to 7.5-8.0 for ATP hydrolysis.
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Affiliation(s)
- F D Moodie
- Department of Biochemistry, King's College, London, England
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Lüthje J. Extracellular adenine compounds, red blood cells and haemostasis: facts and hypotheses. BLUT 1989; 59:367-74. [PMID: 2676021 DOI: 10.1007/bf00321207] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Previously, the role of adenine nucleotides was thought to be confined to the intracellular space of the cell. Research of the last decades has revealed that nucleotides also occur in the extracellular milieu. This survey deals with extracellular adenine compounds in the blood, focussing on their role as chemical mediators in the haemostatic effect of red cells. Erythrocytes may act as pro-aggregatory cells by at least two chemical mechanisms. Firstly, they can enhance platelet aggregation by releasing adenosine diphosphate (ADP), a well known platelet stimulatory substance. ADP is set free when red cells are stressed mechanically, for instance by shear forces generated in the blood stream; ample experimental evidence supporting this view is summarized. Secondly, erythrocytes efficiently take up extracellular adenosine via their nucleoside transporters, thereby removing a potent inhibitor of platelet function. Extracellular adenosine occurs in the blood stream, either directly released from various tissues or as the end product of extracellular adenine nucleotide metabolism, e.g. after degradation of red cell-born ADP or ATP. Finally, a novel mechanism of action of the antithrombotic drug dipyridamole, which has very recently been put forward, is demonstrated. Dipyridamole inhibits platelet function indirectly by blocking the uptake of extracellular adenosine via the nucleoside transporter of red cells; increased adenosine levels in turn are responsible for the antiaggregatory effect of dipyridamole.
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Affiliation(s)
- J Lüthje
- Institut für Biochemie I (Medizinische Fakultät) Universität Erlangen-Nürnberg, Federal Republic of Germany
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Yagi K, Arai Y, Kato N, Hirota K, Miura Y. Purification of ATP diphosphohydrolase from bovine aorta microsomes. EUROPEAN JOURNAL OF BIOCHEMISTRY 1989; 180:509-13. [PMID: 2540963 DOI: 10.1111/j.1432-1033.1989.tb14675.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
ATP diphosphohydrolase (EC 3.6.1.5) hydrolyzes pyrophosphate bonds of nucleoside di- and triphosphates in the presence of divalent cations. We purified the enzyme from the vessel wall of bovine aortas. The procedure gave a homogeneous preparation of ATP diphosphohydrolase for the first time from an animal source. Bovine aorta microsomes were treated with 50 mM bicarbonate buffer (pH 10.0) containing 0.025% Triton X-100. The enzyme was then solubilized from the microsomes with 0.5% Triton X-100 and purified to homogeneity by DEAE-Sepharose CL-6B chromatography and 5'AMP-Sepharose 4B affinity chromatography. The apparent molecular mass of the pure enzyme was 110 kDa. The activity recovered was 6% of that of the microsomes. The enzyme was more active with Ca2+ than Mg2+. The sensitivity of ADPase activity to divalent cations was higher than that of ATPase activity. The enzyme had broad substrate specificity to nucleoside di- and triphosphates.
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Affiliation(s)
- K Yagi
- Department of Biochemical Engineering, Faculty of Pharmaceutical Sciences, Osaka University, Japan
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Lüthje J. Origin, metabolism and function of extracellular adenine nucleotides in the blood. KLINISCHE WOCHENSCHRIFT 1989; 67:317-27. [PMID: 2651791 DOI: 10.1007/bf01741386] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
In previous views the role of adenine nucleotides was thought to be confined to the intracellular space of the cell. However, research of the last decades has revealed that nucleotides also occur in the extracellular space. This survey deals with the sources, metabolism and the role in blood of the extracellular adenine mononucleotides ATP, ADP, AMP and the dinucleotides diadenosine tetraphosphate (Ap4A) and diadenosine triphosphate (Ap3A). The latter two are novel compounds, which have recently been discovered in human platelets. The mononucleotides originate from damaged tissues, from red blood cells during haemolysis, from activated platelets, the working muscle and from the nervous system, whereas the dinucleotides are exclusively released from stimulated platelets. Both the adenine mono- and the dinucleotides act as signal molecules on blood cells as well as on cells of the vascular wall, thereby modulating physiological processes such as platelet aggregation, histamine release from mast cells, regulation of vascular tone and white cell functions. In order to limit the signal effects of extracellular nucleotides, blood cells, plasma and the interior of the vessel walls are provided with nucleotide splitting enzymes: ATP, ADP and AMP are mainly degraded by ectoenzymes present on blood cells, endothelial and on smooth muscle cells, whereas dinucleotides are primarily metabolized by plasma enzymes. This review closes with the presentation of the clinical utility of Ap3A and Ap4A as tools for the diagnosis of platelet storage pool defects.
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Affiliation(s)
- J Lüthje
- Institut für Biochemie I (Medizinische Fakultät) Universität Erlangen-Nürnberg
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Vorbrodt AW. Ultrastructural cytochemistry of blood-brain barrier endothelia. PROGRESS IN HISTOCHEMISTRY AND CYTOCHEMISTRY 1988; 18:1-99. [PMID: 3055069 DOI: 10.1016/s0079-6336(88)80001-9] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- A W Vorbrodt
- New York State Office of Mental Retardation and Developmental Disabilities, Department of Pathological Neurobiology, Staten Island 10314
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Dawson JM, Cook ND, Coade SB, Baum H, Peters TJ. Demonstration of plasma-membrane adenosine diphosphatase activity in rat lung. BIOCHIMICA ET BIOPHYSICA ACTA 1986; 856:566-70. [PMID: 3008836 DOI: 10.1016/0005-2736(86)90148-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The adenosine diphosphatase (ADPase) activity of rat lung has been investigated. Subcellular fractionation of lung tissue homogenates by sucrose density gradient centrifugation has shown the ADPase activity to be associated with the plasma membrane. ADPase was solubilised from the membranes and fractionated by ammonium sulphate precipitation to separate a specific, low-Km ADPase from non-specific alkaline phosphatase activity. The solubilised ADPase has a Km of 50 microM at pH 7.5 and appears to be distinct from ATPase.
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de Vente J, Velema J, Zaagsma J. Properties and subcellular localization of adenosine diphosphatase in rat heart. Arch Biochem Biophys 1984; 233:180-7. [PMID: 6087740 DOI: 10.1016/0003-9861(84)90615-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Some properties and subcellular localization of adenosine diphosphatase (ADPase) activity from rat heart have been investigated. The pH optimum was 7.4, maximal activity was found with 5 mM MgCl2, and the apparent Km was 20 microM. ADPase activity was strongly inhibited by NaF and AppNHp, and to a lesser extent by AMP and GppNHp. The enzyme was not inhibited by p-nitrophenylphosphate, beta-glycerophosphate, or pyridoxal phosphate. The distribution of ADPase activity in subcellular fractions obtained by differential centrifugation parallel ouabain-sensitive (Na+-K+)ATPase and 5'-nucleotidase activities, suggesting a plasma membrane-bound localization. The functional significance of ADPase in adenosine production and hemostasis is discussed.
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Schiavon R, Freeman GE, Guidi GC, Perona G, Zatti M, Kakkar VV. Selenium enhances prostacyclin production by cultured endothelial cells: possible explanation for increased bleeding times in volunteers taking selenium as a dietary supplement. Thromb Res 1984; 34:389-96. [PMID: 6377571 DOI: 10.1016/0049-3848(84)90243-3] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Selenium added to the culture medium of confluent pig aortic endothelial cells caused a time-related elevation in the activity of the hydroperoxide scavenging enzyme: glutathione peroxidase. This increased activity was associated with an enhanced ability to produce prostacyclin irregardless of whether the agonist was arachidonic acid or thrombin. Since prostacyclin synthetase is believed to be irreversibly inhibited by alkyl hydroperoxides, we feel that the greater production of prostacyclin by selenium-treated cells as compared with control cells may reflect a protective effect of GSH.Px towards the synthetase enzyme. The results from this study may explain the observations made on a group of human volunteers ingesting selenium as a dietary supplement. After six weeks treatment with selenium, bleeding time in this group was prolonged suggesting an improved ability to synthesize prostacyclin as a result of selenium-dependent glutathione peroxidase activation in the vessel wall.
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Leake DS, Lieberman GE, Peters TJ. Properties and subcellular localization of adenosine diphosphatase in arterial smooth muscle cells in culture. BIOCHIMICA ET BIOPHYSICA ACTA 1983; 762:52-7. [PMID: 6299383 DOI: 10.1016/0167-4889(83)90116-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The properties and subcellular localization of adenosine diphosphatase (ADPase) activity in smooth muscle cells cultured from pig aortas have been investigated. The pH optimum of ADPase activity was 7.3 and the apparent Km for ADP was 10.3 microM. ADPase activity was inhibited completely by EDTA and was restored by the addition of divalent cations. The enzyme activity was not inhibited by 2-glycerophosphate, a substrate for non-specific phosphatases, nor by levamisole, a specific inhibitor of alkaline phosphatase. Smooth muscle cells were homogenized and a post-nuclear supernatant was applied to a sucrose density gradient in a Beaufay automatic zonal rotor. The distribution of ADPase activity in the density gradient was similar to that of 5'-nucleotidase activity, a marker enzyme for the plasma membrane, and distinct from the distributions of the marker enzymes for the other organelles. When the cells were homogenized in the presence of digitonin, an agent which binds to cholesterol and increases the equilibrium density of the plasma membrane, the modal equilibrium densities of ADPase activity and of 5'-nucleotidase activity were increased to similar extents, thus confirming the plasma membrane localization of ADPase activity.
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Richardson DJ, Smith GP, Meade TW, Langley P, Peters TJ. Assay, kinetics and properties of plasma adenosine diphosphatase. The relationship to acid and alkaline phosphatase and variations in disease. Clin Chim Acta 1982; 121:87-94. [PMID: 6282501 DOI: 10.1016/0009-8981(82)90214-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
A rapid radioassay was used to characterise the adenosine diphosphatase (ADPase) activities in human plasma. There was a major peak at pH 9.3, 80% of whose activity was attributable to non-specific alkaline phosphatase, with the remaining 20% probably due to a specific ADPase. There was also a small peak of ADPase activity at pH 4.0. Inhibitor and chromatographic studies showed that whilst much of this activity was attributable to non-specific acid phosphatase, there was a discrete acid ADPase. Assays of plasma ADPase activities in vascular disorders, including myocardial infarction, peripheral vascular disease and diabetes mellitus, reveal no alterations from control values. Activities of alkaline ADPase were elevated in both chronic and acute liver failure. Acid ADPase was also increased in chronic liver disease and it is suggested that alterations in ADPase activities in liver disorders may contribute to the haemostatic problems observed in these patients.
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