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 re active blue-2 (RB-2), a selective antagonist of the P-(2Y) purinocepto r, at concentrations of 0.3-10 mu M and suramin, a non-selective P-2 p urinoceptor antagonist, at 1-30 mu M blocked the ATP-induced oscillati on in a concentration-dependent manner. 3 RB-2 and suramin also blocke d the ADP-induced K+-current oscillation at the same concentration ran ge 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+ curren t oscillation, indicating that they act as specific purinoceptor antag onists. 4 Thus, the purinoceptors on megakaryocytes show the propertie s of the P-2 subtype according to their blockade by antagonists.