Effect of PAI-1 and PAI-1–derived peptide on the vasoactivity of tPA. (A) EC₅₀ of PE on the contraction of isolated aorta rings was determined in the absence (Control) or presence of tPA 1 nM (tPA 1 nM) or 20 nM (tPA 20 nM), tPA with an equimolar concentration of PAI-1 (tPA 1 nM + PAI-1), (tPA 20 nM + PAI-1), tPA with 2 μM EEIIMD (tPA 1 nM + EEIIMD), (tPA 20 nM + EEIIMD), 20 nM PAI-1 (PAI-1), or 2 μM EEIIMD (EEIIMD) alone. (B) Inhibition of the binding of PAI-1 to tPA by the PAI-1–derived peptide. The binding of PAI-1 (1 nM) to immobilized tPA was determined in the absence (cont.) or presence of 2 μM EEIIMD (EEIIMD). Equimolar concentration of tPA (tPA) served as a positive control. (C) PAI-1–derived peptide enhances LRP-mediated degradation of tPA. The degradation of WT tPA (tPA) or TNK-tPA (TNK-tPA) by SMCs was determined in the absence or presence of PAI-1 (PAI-1) or PAI-1–derived peptide (EE) and of anti-LRP antibodies (anti-LRP) (as specified in the labels).