Unique distribution of glycoprotein receptors on parenchymal and sinusoidal cells of rat liver

Rat hepatocytes and hepatic sinusoidal lining cells (Kupffer and endothelial) were examined for their ability to bind several derivatives of the serum glycoprotein, orosomucoid, in which the carbohydrate chains had been treated with purified neuraminidase, β-D-galactosidase, or β-D-N-acetylglucosaminidase to expose galactose, N-acetylglucosamine or mannose as the terminal, nonreducing sugar constituent. ¹²⁵I-labeled orosomucoid derivatives, as well as ¹²⁵I-labeled mannan, were rapidly cleared from plasma by the liver after intravenous administration. Subsequent recovery of the several radiolabeled ligands from parenchymal and nonparenchymal cells revealed a specific pattern of cellular recognition and incorporation. Whereas galactose-terminated orosomucoid (asialo-orosomucoid) was found preferentially in hepatocytes, glycoproteins terminating in N-acetylglucosamine or mannose were recovered largely in the sinusoidal cells. To corroborate these findings isolated hepatocytes and sinusoidal lining cells were examined in vitro for their ability to recognize the specific radiolabeled derivatives. Intact hepatocytes demonstrated a marked ability to incorporate asialo-orosomucoid. However, no significant binding activity was observed for either N-acetylglucosamine- or mannose-terminated derivatives of orosomucoid. Sinusoidal cells, prepared by pronase digestion, appeared to be devoid of all binding activity. A modification of the isolation procedure for these nonparenchymal cells, employing Metrizamide as a density gradient material, resulted in a preparation which exhibited binding for N-acetylglucosamine- and mannose-terminated glycoproteins but no detectable binding for asialo-orosomucoid. Presumptive evidence is provided by carrier dilution studies for a mannose-specific receptor on sinusoidal cells.