HAG and JW480 inhibit dense granule secretion in human platelets. (A) Washed human platelets (300 × 109/L) were pretreated with the indicated concentrations of HAG, HG, JW480, or DMSO vehicle control (0.5%, not shown) for 30 minutes at room temperature before warming to 37°C for the last 5 minutes. Aggregation was initiated with 1 to 2 μg/mL collagen, and secretion of ATP was measured with the CHRONO-LUME reagent, which was added 2 minutes prior to agonist. The results are normalized to DMSO-treated controls, which were set to 100% (*P < .05 for HAG or JW480 vs HG, n = 4). (B-C) Washed human platelets were pretreated with 10 μM JW480, 10 μM HAG, or DMSO (0.5%) for 30 minutes at 37°C before addition of 0.375 to 1.0 μg/mL collagen. For the indicated samples, ADP (10 μM) was added immediately after collagen, and platelet aggregation (B; ***P < .001, n = 6) or secretion (C; ***P < .001, n = 3) was measured for 3 minutes. n.s., not significant.