Increased platelet integrin activation, α-granule secretion, aggregation, and decreased receptor desensitization in GRK2^−/− mice under ADP stimulation. (A) Platelets from GRK2^−/− and littermate control (WT) mice were stained with fluorophore-conjugated antibodies to either activated integrin α_IIbβ₃ (Jon/A antibody) or P-selectin and measured by flow cytometry. Platelets were stimulated with ADP, TxA₂ mimetic (U46619), PAR4-AP (AYPGKF), or convulxin at the concentrations indicated (n = 4). (B) Platelet aggregation in response to a PAR4-AP or ADP at the concentrations indicated (n ≥ 3). (C) Receptor desensitization measured by platelet aggregation in response to ADP. (Ci) Platelets from GRK2^−/− and littermate WT control mice were stimulated with 5 µM ADP after pre-incubation with 5 µM ADP. (Cii) Platelets from GRK2^−/− and littermate WT control mice were stimulated with 5 µM ADP first and restimulated with 5 µM ADP after a 40-minute interval. n = 4. P ≤ .05 was considered statistically significant. MFI, mean fluorescence intensity; ns, not significant.