ADP-induced platelet aggregation and intracellular Ca²⁺ release. (A) ADP (10 µM)–induced platelet aggregation in human PRP after 30-minute incubation at 30°C with ticagrelor (IC₅₀ = 0.27 μM [0.14-0.51]; n = 3), AR-C 66096 (IC₅₀ = 0.16 μM [0.08-0.33]; n = 4), or R-138727 (IC₅₀ = 3.82 μM [3.03-4.82]; n = 6). The 95% confidence intervals for IC₅₀ values are shown in square brackets. (B) ADP-induced Ca²⁺ peak responses in Fura-2 AM–loaded platelets in the presence of vehicle (n = 16) or 10 µM ticagrelor (n = 22), AR-C 66096 (n = 12), or R-138727 (n = 12). Baseline readings were recorded over a period of 5 cycles (each cycle ∼7 seconds) before ADP addition, after which recording was continued for a further 15 cycles. The peak Ca²⁺ response was determined by calculating the change in fluorescence ratio (340 nm/380 nm). (C) ADP (100 µM)–induced platelet peak Ca²⁺ responses in the presence of vehicle (0.1% DMSO), ticagrelor (10 µM), ticagrelor (10 µM) + XAC (10 µM), AR-C 66096 (10 µM), and R-138727 (10 µM). Data displayed as mean and standard error of the mean (SEM). *P < .05. IC₅₀, 50% inhibitory concentration.