Ultrastructural immunonanogold localization of VAMP-3 in resting and activated human platelets. (A) Resting platelets demonstrate VAMP-3 staining primarily on platelet α-granules. Occasional staining is observed on membranes of the OCS. No staining of VAMP-3 on the extracellular surface is observed. (B) SFLLRN-stimulated and (C) PMA-stimulated platelets do not demonstrate VAMP-3 on their extracellular surface. Bars, 0.5 μm. See “Materials and methods, Immunofluorescence microscopy” for image acquisition information.