Uptake mechanism of fractioned [(3)H]heparin in isolated rat kupffer cells: involvement of scavenger receptors.
The uptake of fractionated [(3)H]heparin was examined to elucidate the uptake mechanism in isolated rat Kupffer cells. The equilibrium binding of fractionated [(3)H]heparin to Kupffer cells was concentration-dependent with the dissociation constant of 5.7 nM and the maximum binding capacity of 1.5 pmol/10(6) cells. Several ligands of scavenger receptors inhibited the binding of fractionated [(3)H]heparin to Kupffer cells competitively and also the internalization of heparin, suggesting the involvement of scavenger receptors in the uptake of fractionated [(3)H]heparin. Fractionated [(3)H]heparin was also suggested to be internalized according to first order kinetics with the apparent internalization rate constant of 0.010 min (-1). Lowering temperature from 37 to 4 degrees C reduced the fraction internalized from 33% to 6% without affecting the total association, while the fraction internalized at 25 degrees C was comparable with that at 37 degrees C. Metabolic inhibitors (2,4-dinitrophenol and rotenone), an inhibitor of receptor-mediated and adsorptive endocytosis of polypeptides (phenylarsine oxide) and phagocytosis inhibitors (cytochalasine B and colchicine) did not inhibit the internalization of fractionated [3(H)]heparin. As known inhibitors of receptor-mediated and adsorptive endocytosis of polypeptides and phagocytosis did not affect the uptake of fractionated heparin, the scavenger receptor-mediated uptake is suggested to be ATP-independent and different from receptor-mediated and adsorptive endocytosis of polypeptides and phagocytosis, although for temperature dependency it showed the typical characteristics of receptor-mediated endocytosis.
Watanabe
J
J
Department of Biopharmaceutics, Faculty of Pharmaceutical Sciences, Nagoya City University, Japan.
Haba
M
M
Urano
K
K
Yuasa
H
H
D019297:2,4-Dinitrophenol / Q000494:pharmacology; D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D003571:Cytochalasin B / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006493:Heparin / Q000378:metabolism*; D007700:Kinetics; D007728:Kupffer Cells; D008024:Ligands; D008099:Liver / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins; D010587:Phagocytosis / Q000187:drug effects / Q000502:physiology; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D011971:Receptors, Immunologic / Q000378:metabolism*; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D012402:Rotenone / Q000494:pharmacology; D051122:Scavenger Receptors, Class B; D013696:Temperature; D014475:Uncoupling Agents / Q000494:pharmacology
D001152:Arsenicals; D004791:Enzyme Inhibitors; D008024:Ligands; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D014475:Uncoupling Agents; D012402:Rotenone; C029341:oxophenylarsine; D003571:Cytochalasin B; D006493:Heparin; D019297:2,4-Dinitrophenol