Effect of platelet adhesion on tyrosine phosphorylation in HUVECs. HUVECs were exposed to hypoxia (4 hours, 1 vol% O₂) and reoxygenation (1 hour; 21 vol% O₂, 5 vol% CO₂). Upon onset of reoxygenation, 2 mL PBS (group 1), PBS containing isolated platelets (150 × 10⁶platelets/mL), or platelets plus fibrinogen (500 mg/dL) were added to the HUVECs and incubated for 60 minutes (for details see Materials and Methods). HUVECs without hypoxia/reoxygenation served as controls.