Adenosine transporters in vascular smooth muscle and endothelium: Multiple [3H]Nitrobenzylthioinosine binding sites in human umbilical vein endothelium

Abstract

AbstractCultured vascular smooth muscle and endothelial cells may be useful models for studying the cardiovascular adenosine transport system and metabolism. We have quantified the nucleoside transporter elements of cultured primate vascular smooth muscle, bovine aortic endothelial, and human umbilical vein endothelial cells by radioligand binding and by using membrane preparations of these cells and the nucleoside transporter probe nitrobenzylthioinosine ([3H]NBMPR), a potent and tightly bound inhibitor of nucleoside transport. The binding was rapid, reversible, saturable, and site‐specific. Scatchard analysis of the saturation data showed that [3H]NBMPR bound to high and low affinity binding sites in human umbilical vein endothelial cell membranes with apparent binding affinities (KD) of 0.093±0.01 nM 1.92±0.1 nM, and binding site densities (Bmax values) of 13.48±1.2 and 69+5.3 fmol/mg protein, respectively. In contrast, the binding to primate vascular smooth muscle and bovine aortic endothelial cell membranes occurred to an apparently high affinity single class of binding sites at which the KD was 1.4±0.3nM and 0.28±0.05nM, respectively, and which had Bmax values of 1,977±163 and 1,284±267 fmol/mg protein, respectively. Scatchard analysis of the binding inhibition by dipyridamole showed a mixed type inhibition, while NBMPR inhibited the binding competitively. Several recognized nucleoside transport inhibitors and vasodilators inhibited the binding with an order of potency similar to that observed for the inhibition of [3H]NBMPR binding to guinea pig cardiac membranes.