PECAM-1–deficient platelets form larger thrombi on a collagen matrix under physiological flow conditions.

Whole blood obtained from PECAM-1^+/+ control mice or PECAM-1–deficient (PECAM-1^−/−) mice were labeled with a fluorescent probe, DiOC₆ (1 μM) for 10 minutes and perfused through collagen-coated (2.5 mg/mL) microcapillary tubes at a wall shear rate of 1800 seconds⁻¹. (A) Thrombi were imaged after 5 minutes of blood flow by confocal microscopy (×100; 1-μm sections), and thrombus volume was determined by quantifying the surface area of each section using the image analysis software package ImageTool (University of Texas Health and Science Center at San Antonio) multiplied by the z height. These results are expressed as a percentage of PECAM-1^+/+ controls (mean ± SEM;P < .05; n = 15). (B, C) Thrombi were imaged at 0.5-, 1.0-, 1.5-, 2.0-, 3.0-, 4.0-, and 5.0-minute time points of blood perfusion by confocal microscopy (×100; 1-μm sections), and thrombus volume was analyzed (B). Results presented in panel B show calculated thrombus volume versus perfusion time for PECAM-1^+/+(■) (solid line) and PECAM-1^−/− (▴) (dashed line) platelets represented as the mean ± SEM from an experiment performed using the blood of 4 individual mice. (C) Representative thrombi were reconstructed in 3-D using Voxblast image analysis software package (Vaytek). The upper panel represents an oblique view of the thrombi, illustrating thrombi surface coverage, and the lower panel represents a cross-section of the thrombi, illustrating thrombi height. All confocal images were taken from planes equidistant from the microcapillary inlet.