Intraplatelet TF is exposed on the surface of activated platelets and microparticles. (A) (i) In thin sections of suspensions of platelets stimulated with collagen and thrombin, TF is visualized by immunoelectronmicroscopy. TF is located on the plasma membrane of the platelets (P) as well as on their pseudopodia (ps; arrows). The identity of the pseudopodia was verified by analyzing a panel of serial thin sections, which indicated their connection with the platelets. In nondegranulating platelets, TF is located within the membrane of the α-granules (arrowheads). (ii) Direct visualization of the degranulation of an α-granule, resulting in the translocation of TF to the cell surface. The panel represents the magnification of the inset marked in the upper panel. Arrows indicate surface TF, whereas arrowheads indicate intraplatelet TF. (B) Virtual absence of TF staining in immunoelectronmicrographs of rapidly prepared neutrophils. The arrow indicates a single gold particle. N indicates nucleus. Note the different diameter scale compared with panel A.