Surface expression of P-selectin on platelets and fibrinogen binding to platelets induced by GP VI stimulation. (A-B) P-selectin expression was detected using FITC-conjugated antimouse P-selectin antibody (A) and analyzed by flow cytometry (B). (C-D) Fibrinogen binding was detected using activated integrin α_IIbβ₃ and binding of Alexa Fluor 488-conjugated human fibrinogen (C) and analyzed by flow cytometry (D). Washed wild-type (WT) and p85α–/– platelets suspended in modified Tyrode-HEPES buffer containing apyrase and RGDS peptide with 1 mM CaCl₂ (A-B) or modified Tyrode-HEPES buffer containing apyrase with 1 mM CaCl₂ (C-D) were stimulated by CRP. Data are from 1 experiment but are representative of 3 independent experiments. In panels B and D, • indicates WT platelets and ▴ indicates p85α–/– platelets.