Effect of RO318220 on annexin V binding to thrombin-stimulated platelets. Flow cytometry detected the binding of FITC-labeled annexin V to thrombin-stimulated gel-filtered platelets treated with DMSO (A) or 20 (B), 50 (C), or 100 (D) μM RO318220. Histograms depict the platelet population negative for annexin V in M1, the control platelet population highly positive for annexin V in M4, and the arrow follows the peak positive fluorescence as it moves toward the negative marker with increasing RO318220 treatment. The platelet population was defined by FITC-anti-glycoprotein 1bα (GP1bα) binding. Negative controls containing EDTA were used to set the positive window for FITC-annexin V.