Effects of platelet SR-BI deficiency on the platelet reactivity, platelet cholesterol content, platelet counts, and thrombosis in hyperlipidemic conditions of SR-BI^−/− mice. (A) Platelets in PRP from chimeric SR-BI^−/− mice with SR-BI^−/− bone marrow (BM) or WT BM were stimulated with ADP, PAR4-AP, or convulxin (CVX). Platelet integrin α_IIbβ₃ activation was determined by FACS analysis (n ≥ 3). (B-C) Platelet aggregation in PRP from SR-BI^−/− mice with SR-BI^−/− BM or WT BM was induced by 120μM PAR4-AP and was optically monitored. (B) Quantification of the aggregation data. Data are expressed as maximal amplitude of aggregation within 5 minutes after adding the agonist (n ≥ 3). (C) Representative aggregation curves are shown. (D) Platelet cholesterol contents for chimeric SR-BI^−/− mice with WT or SR-BI^−/− BM. Platelets were stained with 50 μg/mL filipin and analyzed by flow cytometry (n ≥ 3). (E) Times to thrombotic occlusion of carotid arteries of chimeric SR-BI^−/− mice with SR-BI^−/− BM or WT BM were measured 2 minutes after topical application of 10% FeCl₃. Carotid arteries were visualized, and in vivo thrombosis formation was assessed by intravital microscopy as described in “Methods” n = 7. (F) Progression of thrombus in carotid arteries is shown. Times after FeCl₃-induced injury are indicated (in minutes). At 10 minutes, the artery from the SR-BI^−/− (WT BM) mice was completely occluded, whereas the SR-BI^−/− (SR-BI^−/− BM) mice showed large thrombi with persistent blood flow. All images were observed under a Leica DM LFS microscope (Leica) with 10×/0.30 objective lens and acquired by a cooled high-speed, color, cooled digital camera (QImaging Retiga EXi Fast 1394) with Streampix high-speed acquisition software. (G-H) Platelet counts in whole blood collected from chimeric SR-BI^−/− mice with SR-BI^−/− BM or WT BM and from chimeric WT mice with WT BM in panel G, as well as from WT or SR-BI^−/− mice in panel H. n ≥ 5. All data are presented as mean ± SEM. *P < .05, **P < .01, ***P < .001.