Preclustered receptor arrangement is a prerequisite for galactose-specific clearance of large particulate ligands in rat liver.

We had hypothesized that preclustered arrangement of galactose-specific receptor activity on rat liver macrophages enables these cells to internalize multivalent, particulate ligands in contrast to the clearance of molecules mediated by statistically distributed receptors on hepatocytes. We now took advantage of the nonclustered receptor distribution in newborn rat liver macrophages to study the in vivo clearance of particulate ligands. Gold particles 5, 17, and 50 nm in diameter (Au5, Au17, Au50), coated with lactosylated bovine serum albumin (LacBSA), were injected into the vena cava and livers were perfusion fixed after allowing for binding and uptake for 3 min. In sinusoidal cells from rats 15 days old LacBSA-Au5 and LacBSA-Au17 were taken up by endothelial cells and all sizes by liver macrophages. In newborn rat liver no LacBSA-Au50 or LacBSA-Au17 was retained in liver macrophages. Uptake of LacBSA-Au5 by sinusoidal cells was significant. LacBSA-Au17 was taken up in significant amounts by endothelial cells of newborn rats which correlates to the findings that galactose-specific binding sites on endothelial cells were found to localize as clusters over coated pits irrespective of age. These results demonstrate the crucial role of clustered receptors in binding and uptake of larger particulate ligands via this lectin-like binding activity.