SURAMIN AND REACTIVE BLUE-2 ARE ANTAGONISTS FOR A NEWLY IDENTIFIED PURINOCEPTOR ON RAT MEGAKARYOCYTE

1 The effects of purinoceptor antagonists on ATP-induced oscillatory K+-currents in rat isolated megakaryocytes were investigated. 2 Both reactive blue-2 (RB-2), a selective antagonist of the P-(2Y) purinoceptor, at concentrations of 0.3-10 mu M and suramin, a non-selective P-2 purinoceptor antagonist, at 1-30 mu M blocked the ATP-induced oscillation in a concentration-dependent manner. 3 RB-2 and suramin also blocked the ADP-induced K+-current oscillation at the same concentration range as in the case of ATP. However, both suramin and RB-2 had no effect on thrombin- and inositol 1,4,5-trisphosphate (IP3)-induced K+ current oscillation, indicating that they act as specific purinoceptor antagonists. 4 Thus, the purinoceptors on megakaryocytes show the properties of the P-2 subtype according to their blockade by antagonists.