Uptake of asialo-glycophorin by the perfused rat liver and isolated hepatocytes.

Perfused rat livers took up asialo-glycophorin, a glycoprotein derived from human erythrocyte membranes, with a t1/2 for clearance of 7 min. As a comparison, asialo-orosomucoid was taken up by this system with a t1/2 of 3.5 min. Both proiteins were digested and their 125I labels were released to the perfusate as free 125I-. EGTA completely inhibited uptake of these glycoproteins, but not uptake of denatured bovine serum albumin. Addition of Ca2+ reversed the inhibition nearly completely. Isolated hepatocytes had an uptake rate of approximately 3 ng/min per 10(6) cells for the asialo forms of glycophorin, orosomucoid and fetuin. Cellular uptake of each of these asialoglycoproteins could be inhibited by one of the other proteins. Asialo-fetuin caused a 95% inhibition of the uptake rate of asialo-orosomucoid by the perfused liver. This fetal calf glycoprotein had a similar inhibitory effect on asialo-glycophorin, but only after an initial 40% of the asialo-glycophorin had been taken up by the liver at an almost normal rate during the first 30 min of perfsuion. The possibility of an alternative hepatic removal system for asialo-glycophorin is suggested.