title: Evidence supporting the Nucleotide Axis Hypothesis: ATP release and metabolism by coronary endothelium.
abstract: The Nucleotide Axis Hypothesis, defined and supported herein, proposes that ATP stimulates the release of vasoactive mediators from endothelium, including ATP itself. Here, we show rapid endothelium-dependent, agonist-stimulated ATP elaboration in coronary vessels of guinea pigs. Measurement of extracellular ADP metabolism in intact vessels results in the time- and substrate-dependent formation of ATP in the coronary perfusate in amounts greater than can be accounted for by release from endothelium alone. ATP formation by endothelial cells is saturable (K(M) = 38.5 micromol/l, where K(M) is substrate concentration at which rate is half-maximal.) and trypsin-sensitive, membranes from [gamma-(32)P]ATP-labeled cells support ADP-dependent transphosphorylation by a 20-kDa protein, Western blots reveal the presence of a nucleoside diphosphate kinase (NDPK) of approximately 20 kDa in endothelial membranes, and analysis of NDPK antibody binding by flow cytometry is consistent with the presence of an ecto-NDPK on cardiac endothelial cells. Sequencing of the endothelial cell ecto-NDPK reveals a predicted amino acid sequence with 85% identity to human Nm23-H1 and consistent with a protein whose properties may confer membrane association as well as sites of regulation of activity. Our data underscore the potential importance of a nucleotide axis in cardiac blood vessels.
authors.affiliation: Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada 89557, USA.
authors.forename: I L
authors.initials: IL
authors.lastname: Buxton
authors.forename: R A
authors.initials: RA
authors.lastname: Kaiser
authors.forename: B C
authors.initials: BC
authors.lastname: Oxhorn
authors.forename: D J
authors.initials: DJ
authors.lastname: Cheek
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001920:Bradykinin / Q000502:physiology; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000166:cytology / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D008955:Models, Cardiovascular; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics; D054778:NM23 Nucleoside Diphosphate Kinases; D009701:Nucleoside-Diphosphate Kinase / Q000378:metabolism; D009711:Nucleotides / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics
chemical_list: D054778:NM23 Nucleoside Diphosphate Kinases; D009711:Nucleotides; D014157:Transcription Factors; D000255:Adenosine Triphosphate; C517938:NME1 protein, human; D009701:Nucleoside-Diphosphate Kinase; D020559:Monomeric GTP-Binding Proteins; D001920:Bradykinin