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, pyridoxalyphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) could distinguish between these two receptor subtypes. 2 Cells labelled with myo-[2-H-3]-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 mu M PPADS. The accumulation of total [H-3]-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 mu 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.