Strong activation of P2cyc results in aggregation of Gαq-deficient mouse platelets.

(A) Addition of ADP (100 μmol/L) to a stirred suspension of Gαq-deficient washed platelets resulted in a gradual increase in light transmission owing to the formation of optically visible small aggregates. (B) This effect of ADP was blocked by AR-C69931MX (10 μmol/L) or clopidogrel (100 mg/kg), suggesting that it is mediated by the P2cyc receptor. (C) The P2cyc-induced platelet aggregation was integrin dependent since it was blocked by an antimouse integrin αIIbβ3 antibody. (D) Adrenaline (100 μmol/L) was unable to induce the same effect as ADP.