Role of VASP in the regulation of platelet adhesion in the common carotid artery in vivo. (A) Platelet–endothelial cell interactions were investigated in VASP^–/– mice by in vivo fluorescence microscopy of the common carotid artery in situ. Wild-type animals served as controls. The panels summarize platelet tethering (left) and firm platelet adhesion (right). Tethered and adherent platelets were classified according to their interaction with the endothelial cell lining as described in “Materials and methods” and are given per mm² of vessel surface. Mean ± SEM, n = 8-10 each group; * indicates significant difference compared with wild-type mice; P < .05. (B) The microphotographs show representative in vivo fluorescence microscopy images. White arrows indicate adherent platelets. Bars represent 50 μm. Role of P-selectin and GPIIb-IIIa for platelet tethering (C) and firm platelet adhesion (D) in VASP null mice. VASP^–/– mice were injected with 50 μg function-blocking anti–P-selectin or anti–GPIIb-IIIa mAb, respectively, prior to in vivo videofluorescence microscopy. Untreated VASP null mice served as controls. Tethered and adherent platelets were classified according to their interaction with the endothelial cell lining as described in “Materials and methods” and are given per mm² of vessel surface. Mean ± SEM; n = 6-7 carotid arteries; * indicates significant difference compared with untreated VASP null mice; P < .05.