Platelet adhesion following endothelial denudation. (A) Scanning electron micrographs of carotid arteries prior to (left) and after (right) vascular injury. Endothelial denudation induces platelet adhesion. Bars represent 5 μm. (B-C) Fluorescent wild-type or VASP^–/– platelets were preincubated with either PBS (Control) or the NO-donor spermine-NO. After preincubation, the samples were stimulated with 0.2 U/mL mouse thrombin or with PBS. Platelet tethering (B) and firm platelet adhesion (C) to the carotid artery were assessed by intravital videofluorescence microscopy. Mean ± SEM; n = 5 each group; * indicates significant difference compared with control; ns indicates no significant difference; P < .05. (D) The microphotographs show representative in vivo fluorescence microscopy images in illustrating adhesion of wild-type or VASP^–/– platelets following endothelial denudation in the absence or presence of spermine-NO. Bars represent 50 μm. (E) Role of GPIIb-IIIa for tethering and adhesion of VASP null platelets following endothelial denudation. Wild-type mice were injected with VASP^–/– platelets preincubated with 50 μg function-blocking anti–GPIIb-IIIa mAb. Platelet recruitment was visualized at the site of injury by videofluorescence microscopy. The graph shows percent inhibition of platelet tethering and adhesion by anti–GPIIb-IIIa mAb (n = 5) compared with PBS-treated mice (n = 4). Mean ± SEM.