EXOC3 KO platelets elicit hyperactive responses to stimulation with PAR4-AP. (A-B) Washed platelets (2 × 10⁸/mL) from WT and EXOC3 KO platelets were stimulated with increasing concentrations of PAR4-AP and monitored for changes in platelet aggregation and dense granule secretion. Representative aggregation (Ai-iii) and secretion (Aiv-vi) traces are shown. Quantified area under the curve (AUC) (Bi) and peak ATP (Bii) values were calculated to assess aggregation and secretion responses, respectively. (C) Washed platelets (2 × 10⁷/mL) from WT and EXOC3 KO mice were treated with indicated concentrations of PAR4-AP (50-300 µM) for 10 minutes, fixed and analyzed for JON/A binding (i) and P-selectin surface exposure (CD62P) (ii) by using flow cytometry. (D) Similar to panel C, washed platelets were stimulated with PAR4-AP (300 µM) or thrombin (1 U/mL) for 10 minutes and monitored for changes in surface CD41 levels. Data are presented as the mean ± standard error of the mean. n = 4-5 (A-B); n = 8 (C); n = 9 (D). **P < .01, ****P < .0001 vs indicated sample.