ADP can induce aggregation of human platelets via both P2Y1 and P2T receptors

In the present study we have investigated the roles of P2Y1 and P2T receptor subtypes in adenosine 5′‐diphosphate (ADP)‐induced aggregation of human platelets in heparinized platelet rich plasma. The response to ADP can be characterized as the initial rate or the maximum or final extent of aggregation. The response profile is determined by the concentration of ADP used, being transient at lower and sustained at higher concentrations. The P2Y1 receptor antagonist, adenosine‐3′‐phosphate‐5′‐phosphate (A3P5P) competitively antagonized the initial rate of aggregation (pKB 5.47) and transformed the response profile to a slowly developing but sustained response. Both maximum and final extents were also inhibited by A3P5P although not in a competitive manner (Schild slope