Binding of soluble fibrinogen to platelets expressing hαIIb/mβ3 is inhibited by RUC-1; WT murine platelets and platelets expressing mαIIb/hβ3 are not inhibited by RUC-1. Whole blood anticoagulated with PPACK from WT mice (n = 4), mice expressing mαIIb/hβ3 (n = 4), or mice expressing hαIIb/mβ3 (n = 4) was diluted in buffer containing 2 mM CaCl2/1 mM MgCl2. Samples were either untreated or treated with 20 or 100 μM RUC-1, and 200 μg/mL fluorescent fibrinogen were added before activating with 200 μM PAR-4 activating peptide. Samples were incubated at 37°C for 30 minutes before diluting and analyzing using flow cytometry. Geometric mean fluorescence intensities of unactivated samples were subtracted as background, and untreated activated samples were used to establish 100% binding (*P = .002, †P < .001).
