PPADS: an antagonist at endothelial P 2Y ‐purinoceptors but not P 2U ‐purinoceptors

1 Bovine aortic endothelial (BAE) cells contain two co‐existing receptors for extracellular ATP, the P 2Y and P 2U ‐purinoceptors. Here we have determined whether the proposed P 2x ‐purinoceptor antagonist, pyridoxalphosphate‐6‐azophenyl‐2″, 4″‐disulphonic acid (PPADS) could distinguish between these two receptor subtypes. 2 Cells labelled with myo ‐[2‐ 3 H]‐inositol were stimulated with increasing concentrations of either the P 2Y ‐agonist, 2MeSATP, or the P 2U ‐agonist, UTP in the absence or presence of 30 μ m PPADS. The accumulation of total [ 3 H]‐inositol (poly)phosphates mediated by 2MeSATP was markedly attenuated by PPADS, whereas the response to UTP was not significantly affected. 3 Stimulation of BAE cells with increasing concentrations of ATP showed a reduced response in the presence of 10 μ m PPADS, but this effect of the antagonist was not significant. By contrast, inhibition of the response to ADP was profound and highly significant. 4 These observations show that PPADS is not a selective P 2X ‐purinoceptor antagonist, but is able to distinguish between P 2Y ‐ and P 2U ‐purinoceptors in BAE cells, and indicate that this compound may provide a useful tool in the study of multiple subtypes of P 2 ‐purinoceptors. Furthermore the results are consistent with the hypothesis that ATP interacts with both receptor subtypes, but that the action of ADP is primarily at the P 2Y ‐purinoceptor in these endothelial cells.