Concentration-dependent effect of plasminogen activators on fibrin degradation of thrombi under flow. Platelet-fibrin thrombi were formed by perfusion (1000 s⁻¹) of whole blood for 7 minutes over collagen/TF in the absence or presence of tPA or uPA (0 nM to 75 nM). Blood samples were pre-incubated with DiOC₆ (0.5 µg/ml) to label platelets and fibrinogen-AF647 (16.7 µg/ml). The fluorescent thrombi were perfused (t = 0) with buffer 1 (HEPES buffer, pH 7.45) for 8 minutes, followed by buffer 2 (HEPES buffer, pH 7.45 with the indicated concentration of tPA or uPA) for up to 28 minutes. Shown are representative images of thrombi labeled for fibrin(ogen) (red), platelets (green), and label overlay (yellow) (left panels). Scale bars represent 50 µm. Also shown is dose-dependent fibrinolysis in time, expressed as fibrin(ogen)-AF647 surface coverage (% of t = 0, ± SEM) (middle panels), and time to 50% lysis (right panels). (A) Absence of plasminogen activators, light bars represent controls where 75 nM tPA or uPA were present in buffer 2 only and not during thrombus formation. (B) tPA-mediated fibrinolysis and (C) uPA-mediated fibrinolysis. Data represent mean ± SEM, *P < .05 vs no tPA or uPA, n ≥ 3.