Inhibition of P-selectin expression, integrin α_IIbβ₃ activation, and ATP release by OxHDL. (A,B) Human platelets isolated by gel filtration (2.5 × 10⁶) in buffer containing 2 mM Ca²⁺ and 1 mM Mg²⁺ were incubated with or without 200 μg/mL HDL or OxHDL for 5 minutes at room temperature, followed by stimulation with 0.1 U/mL thrombin. Samples were incubated either with 1:1000 FITC-conjugated anti–P-selectin antibody (A) or with 1:100 FITC-conjugated anti-α_IIbβ₃ antibody (B) for 15 minutes and analyzed by flow cytometry. (C) Quantification of the data (means ± SEM) as in panels A and B from 5 independent experiments. (D) ATP release was measured in human platelets containing luciferin-luciferase reagent incubated with or without 200 μg/mL HDL or OxHDL for 5 minutes, followed by stimulation with 0.1 U/mL thrombin. (E) Quantification of the data (means ± SD) in panel D from 3 independent experiments. NA indicates no addition. *P < .001.