Cryosections of HUVEC incubated with biotin before endocytosis and fixation. The cell surface labeled with anti-TFPI (large gold) and anti-biotin (small gold). Colocalization of anti-TFPI and anti-biotin was seen in small vesicles close to the cell surface (A, arrow) and in larger vesicles (panel B). Bars = 0.2 μm.