Diadenosine polyphosphates as antagonists of the endogenous P2Y 1 receptor in rat brain capillary endothelial cells of the B7 and B10 clones

Diadenosine polyphosphates (Ap n As, n =2–7) are considered as stress mediators in the cardiovascular system. They act both via identified P2 purinoceptors and via yet to be characterized receptors. This study analyses the actions of Ap n As in clones of rat brain capillary endothelial cells that express P2Y 1 receptors (B10 cells) or both P2Y 1 and P2Y 2 receptors (B7 cells). B10 cells responded to Ap 3 A with rises in intracellular Ca 2+ concentration ([Ca 2+ ] i ). This response was prevented by adenosine‐3′‐phosphate‐5′‐phosphate, an antagonist of P2Y 1 receptors. It was largely suppressed by a treatment with apyrase VII or with creatine phosphokinase/creatine phosphate to degrade contaminating ADP. Ap n As inhibited ADP induced increases in [Ca 2+ ] i mediated by P2Y 1 receptors by shifting ADP concentration‐response curves to larger concentrations. Apparent K i values were estimated to be 6 μ M for Ap 4 A, 10 μ M for Ap 5 A and 47 μ M for Ap 6 A. Ap 2 A and Ap 3 A were much less active. Ap n As were neither agonists nor antagonists of the endogenous P2Y 2 receptor in B7 cells. Ap n As are neither agonists nor antagonists of the G i ‐coupled, ADP receptor in B10 cells. The results suggest that most actions of Ap n As in B7 and B10 cells can be accounted for by endogenous P2Y 1 receptors. Ap 4 A, Ap 5 A and Ap 6 A are specific antagonists of endogenous Ca 2+ ‐coupled P2Y 1 receptors.British Journal of Pharmacology (2000) 129 , 1506–1512; doi: 10.1038/sj.bjp.0703228