Figure 10.

Fate of preinternalized DFP-uPA or uPA:PAI-1 in polarized or nonpolarized MDCK cells in the absence or presence of RAP. Polarized (A) or nonpolarized (B) cells were incubated with 500 pM [¹²⁵I]DFP-uPA or [¹²⁵I]uPA:PAI-1 for 90 min at 4°C in the absence or presence of the indicated concentrations of RAP. After washing on ice, cells were incubated at 37°C for 10 min to allow internalization of ligand. Surface-bound ligand was then removed by acid washing on ice, and cells returned to 37°C for a further 40 min with or without the indicated concentrations of RAP in the presence of 100 nM unlabeled uPA in the incubation medium to prevent reinternalization of recycled ligand. Degraded ligand represented by TCA-soluble counts per minute in the medium (black bars) or recycled ligand recovered on the cell surface or as TCA-insoluble counts in the medium (white bars) were expressed as percentage of counts internalized after the 10-min incubation. Means of two independent experiments in duplicate are shown. Variation was <10%.