Reduced ADP secretion is responsible for defective aggregation of MINK1^−/− platelets. (A,C) Aggregation and ATP release of washed WT or MINK1^−/− platelets stimulated with collagen (0.8 μg/mL) or thrombin (0.025 U/mL) in the presence or absence of apyrase (1 U/mL) incubated for 5 minutes. (B,D) Percentage of platelet aggregation and ATP release from at least 4 independent experiments depicted in panels A and C, and the results are shown as mean ± SEM (*P < .05, **P < .01, ***P < .001, paired Student t test). (E,G) A low concentration of ADP (1 μM), insufficient to induce aggregation on its own, reversed the inhibitory effect of MINK1^−/− platelets on aggregation stimulated with collagen (0.8 μg/mL) or thrombin (0.025 U/mL). (F,H) Percentage of platelet aggregation from at least 4 independent experiments depicted in panels E and G, and the results are shown as mean ± SEM (*P < .05, **P < .01, paired Student t test). ns, no significance.