Characterization of ADAP^−/− platelets. Washed platelets from ADAP^+/+ and ADAP^−/− mice were incubated with the appropriate antibodies, and binding was determined by flow cytometry. (A) αIIbβ3 surface expression. (B) GP Ibα surface expression. (C) α-granule secretion. Platelets were resting, or activated with 250 μM Par4-activating peptide, and the binding of an anti–murine P selectin antibody was determined. There was no statistically significant difference in P selectin expression between ADAP^+/+ and ADAP^−/− platelets in response to Par4-activating peptide despite statistically significant increases in P selectin expression compared with resting platelets. Results shown represent a summary of at least 4 experiments and show the average ligand binding ± standard error of the mean (SEM).