Loss of Δψ_m occurs in a subpopulation of activated platelets. Platelets were left unstimulated or stimulated with thrombin (0.5 U/mL), or thrombin plus convulxin (Cvx) (250 ng/mL), for 5 minutes. (A) Platelet Δψ_m was assessed by flow cytometry using the cationic dye TMRM. TMRM retention within mitochondria is dependent on the maintenance of Δψ_m, and loss of Δψ_m results in decreased TMRM fluorescence. (B-D) Two-color flow cytometry with TMRM and (B) FITC-labeled anti-P-selectin, (C) FITC-labeled annexin V, or (D) FITC-labeled antifibrinogen is demonstrated. Region A1 indicates the subpopulation of activated platelets that retained TMRM staining. Region A2 indicates the subpopulation of activated platelets that lost TMRM staining. Plots are representative of 3 separate experiments.