The effect of p38 and MEK inhibitors on platelet secretion and aggregation. (A,B) Washed platelets were preincubated at 37°C for 2 minutes in the presence of either 10 μM p38 inhibitor, SB203580 (A), 3 μM MEK inhibitor, U0126 (B), or DMSO vehicle control. Platelet aggregation was induced by 0.5 μg/mL collagen in the presence of luciferase reagent, and ATP release was measured using a platelet lumi-aggregometer. (C,D) Washed platelets were preincubated with either SB203580 (C), U0126 (D), or DMSO. Platelets were stimulated with 0.025 U/mL thrombin, and ATP release was measured. (E) Quantification of peak platelet ATP release (in μM, mean ± SD). Statistical significance was determined using Student t test. Platelets were preincubated with either 10 μM SB203580, 3 μM U0126, or vehicle control (F,G); or 30 μM SB203580, PD98059, or vehicle control (H,I), and stimulated with 0.025 U/mL thrombin in the presence or absence of 0.5 μM ADP in a turbdometric aggregometer. Aggregation traces are shown.