RECEPTOR-MEDIATED ENDOCYTOSIS OF CHEMICALLY-MODIFIED ALBUMINS BY SINUSOIDAL ENDOTHELIAL-CELLS AND KUPFFER CELLS IN RAT AND HUMAN LIVER

Human serum albumin (HSA), formaldehyde-treated HSA (FHSA), and HSA po lymerized with glutaraldehyde (pHSA) were conjugated with colloidal go ld (15 (15G) or 50 (50G) nm in diameter). The labeled proteins were in jected into the portal veins of rats and followed by electron microsco py. Both 15G-FHSA and 15G-pHSA were taken up by sinusoidal endothelial cells (Ec) and Kupffer cells (Kc). Five minutes after injection, gold particles were observed on the surface of Ec and Kc. At 10 min, most gold particles were gathered in the coated pits and vesicles of Ec. In Kc, gold particles were observed in both coated vesicles and macropin ocytotic vesicles. At 15 min, the gold particles were localized mainly in the endosomes and some lysosomes of Ec and in the large vacuoles o f Kc. At 30 min, the gold particles had been gathered into the seconda ry lysosomes and condensed. At 60 min, some gold particles were observ ed in the cytoplasm of Ec. The fate of 15G-pHSA was the same as that o f 15G-FHSA. Simultaneous injection of 15G-pHSA and 50G-FHSA revealed t hat particles of both sizes were taken up together into the coated pit s and vesicles of Ec. Preperfusion of livers with unlabeled FHSA, pHSA , or formaldehyde-treated bovine serum albumin (FBSA) inhibited the up take of 15G-FHSA or 15G-pHSA by Ec. In a human liver biopsy specimen, both 15G-FHSA and 15G-pHSA were taken up by Ec and Kc through coated v esicles, as in the rat liver. These results suggest that aldehyde-modi fied albumin is taken up by both Ec and Kc, and that both FHSA and pHS A share a common receptor on Ec.