Uptake of fractionated heparin by two types of scavenger receptors in isolated rat Kupffer cells

The uptake of fractionated heparin was examined in the absence and presence of anionic proteins such as acetylated low destiny lipoprotein (Ac-LDL) an d maleylated bovine serum albumin (Mal-BSA) to characterize the scavenger r eceptors involved in the uptake of fractionated heparin in isolated rat Kup ffer cells. The uptake of fractionated heparin was completely inhibited by Ac-LDL and dextran sulfate, but only partially by Mal-BSA. Kinetic analysis revealed that the binding capacity (B-max) of the Mal-BSA- insensitive receptor was significantly larger than that of the Mal-BSA-sens itive one, though their dissociation constants (K-d) were not significantly different. The apparent internalization rate constant (k(int,app)) was sig nificantly larger for the Mal-BSA-sensitive receptor than for the Mal-BSA-i nsensitive one. Thus, the scavenger receptors involved in the uptake of fra ctionated heparin in Kupffer cells can be classified into two types, in ter ms of sensitivity to Mal-BSA. Mal-BSA-sensiti ve receptors have been charac terized in macrophages and classified as class A. The Mal-BSA-sensitive one found in Kupffer cells in this study may belong to class A, while the Mal- BSA-insensitive one has been little characterized elsewhere.