Continuous ADP-induced signaling via P2Y₁₂ and PI3Kβ is needed for irreversible platelet aggregation. (A) Aggregation of PPACK-anticoagulated PRP was triggered while stirring with 20 μM ADP or 1 μg/mL collagen (n = 3-5). Inhibitors were added after 2 minutes, when aggregation was maximal: indomethacin (55 μM), aggrastat (2 μg/mL), iloprost (20 nM), apyrase (0.2 U/mL), MRS2179 (100 μM), AR-C69931MX (30 μM), wortmannin (1 μM), LY294002 (50 μM), or TGX221 (1 μM). Shown are representative aggregation traces. Arrows indicate addition of inhibitors. (B) Percentages of disaggregation with ADP after 12 minutes; numbers above bars indicate platelet counts (× 10⁹/L). Data are mean ± SEM.