Uptake of fractionated 3H-heparin by isolated rat Kupffer cells

Abstract

Purpose and methods: The uptake of fractionated 3H-heparin by isolated rat Kupffer cells was examined to determine the uptake mechanism.

Results: The association of fractionated 3H-heparin was concentration-dependent with a dissociation constant of 3.4 nM and a maximum association capacity of 1.3 pmol/10(6) cells, suggesting the involvement of a specialized mechanism. Although 2,4-dinitrophenol inhibited neither the association nor internalization of fractionated 3H-heparin, lowering the temperature from 37 degrees C to 4 degrees C reduced the internalization of fractionated 3H-heparin by 70% without affecting the association.

Conclusions: It is suggested that the uptake mechanism may differ from receptor-mediated endocytosis of polypeptides and be mediated by scavenger receptors, because organic anions, and several ligands of scavenger receptors, as well as several heparin analogs, inhibit the binding of fractionated 3H-heparin to Kupffer cells, while phenylarsine oxide, which is known to inhibit the receptor-mediated or absorptive endocytosis of polypeptides, inhibits neither the association nor internalization of fractionated 3H-heparin.