UPTAKE OF HUMAN URINARY TRYPSIN-INHIBITOR BY THE KIDNEY EPITHELIAL-CELL LINE, LLC-PK1

We investigated the uptake of human urinary trypsin inhibitor (UTI) by the kidney epithelial cells, LLC-PK1. Indirect immunogold techniques with an electron microscope demonstrated the localization of UTI withi n the cells after an incubation during which UTI was added to the apic al side. Immunoreactivities were found in endocytic vesicles, vacuoles and lysosomes. Subsequently, we tried to characterize the property of the uptake of UTI using the fluorescein isothiocyanate-labelled UTI ( FITC-UTI). FITC-UTI uptake was decreased by an incubation with an exce ss of unlabelled UTI and showed concentration-dependent saturation. Th is process was markedly suppressed during the incubation at 4 degrees C. The uptake was significantly lessened with 2,4-dinitrophenol and an timycin A, inhibitors of oxidative phosphorylation, and colchicine, a microtubule-depolymerizing agent. These results indicate that exogenou s UTI is internalized by LLC-PK1 cells through an endocytic pathway. F rom uptake studies, it is suggested that an adsorptive process is part ially involved in the mechanisms of endocytosis.