THE RECEPTOR FOR TISSUE PLASMINOGEN-ACTIVATOR (T-PA) IN COMPLEX WITH ITS INHIBITOR, PAI-1, ON HUMAN HEPATOCYTES

The binding of t-PA-PAI-1 to human hepatocytes at 4-degrees-C reached a maximum at 2 h. Scatchard analysis indicated 7400 +/- 11000 high-affinity binding sites for complex per human hepatocyte, with a K(d) of 0.87 +/- 0.09 nM. Almost identical results were achieved with the human hepatoma cell line Hep G2. Binding of [I-125]t-PA-PAI-1 complex was unaffected by high concentrations of unlabelled t-PA, PAI-1, u-PA or u-PA-PAI-1 complex; only t-PA-PAI-1 complex competed for binding. Hepatocyte-bound t-PA-PAI-1 was internalized and degraded at 37-degrees-C. Thus, hepatocytes have a specific t-PA-PAI-1 receptor that participates in clearance of this complex.