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Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada 89557
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
(KM = 38.5 µmol/l, where
KM is substrate concentration at which rate is
half-maximal.) and trypsin-sensitive, membranes from
[
-32P]ATP-labeled cells support ADP-dependent
transphosphorylation by a 20-kDa protein, Western blots reveal the
presence of a nucleoside diphosphate kinase (NDPK) of ~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.
release of vasoactive factors; ectoenzyme; ecto-Nm23
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