Granule secretion mediated by FcγRIIa activation is regulated by 12-LOX. Washed human platelets treated with DMSO or ML355 were stimulated by FcγRIIa crosslinking in which IV.3 (2 μg/mL) + GAM (10 μg/mL) were used for (A) α-granule secretion. α-granule secretion was measured by using P-selectin-PE conjugated antibody in a flow cytometer. To obtain the percentage of platelets that were positive for P-selectin, approximately 10% of the unstimulated platelet population was gated (as shown in histogram), and then applied to ML355- and DMSO-treated platelets in order to quantify the percentage of platelets that were positive for P-selectin. A composite bar graph shows the percentage of platelets positive for P-selectin in ML355- and DMSO-treated platelets (n = 5). (B) IV.3 (2 μg/mL) + GAM (5 μg/mL) were used to stimulate ATP secretion as a surrogate marker for dense granule secretion in a lumi-aggregometer. A bar graph of DMSO- or ML355-treated platelets measured for ATP secretion following FcγRIIa crosslinking (n = 4) is shown. Error bars indicate SEM. **P < .01.