ROLE OF CYTOSKELETON AND ACIDIFICATION OF ENDOCYTIC COMPARTMENT IN ASIALOGLYCOPROTEIN METABOLISM IN ISOLATED RAT HEPATOCYTE COUPLETS

The process of receptor-mediated endocytosis is common to a variety of species and cell types. One of the best characterized receptor-ligand systems is the hepatocyte receptor for asialoglycoproteins. We invest igated the morphological features of the uptake and intracellular tran sport of gold-conjugated asialofetuin in isolated rat hepatocyte coupl ets. We assessed the effects of colchicine, lumicolchicine, cytochalas in B, and chloroquine on the uptake and intracellular transport of asi aloglycoproteins. Isolated rat hepatocyte couplets were incubated with gold-conjugated asialofetuin, and transmission electron micrographs o f these cells were analyzed to determine the density and distribution of gold particles in the peripheral and pericanalicular areas. Results were analyzed morphometrically. Colchicine significantly inhibited th e uptake and intracellular transport of asialoglycoproteins, but did n ot affect membrane fusion of endocytic compartments in the peripheral area. Lumicolchicine and cytochalasin B had minimal effects on these p rocesses. Chloroquine inhibited the uptake of asialoglycoproteins, but did not affect the intracellular transport of asialoglycoproteins. Re sults suggest that the microtubule is essential for intracellular move ment of endocytosed asialoglycoproteins and receptor recycling, and th at endocytic structures in the peripheral regions can fuse in the abse nce of intact microtubules. We also found that uptake and intracellula r transport of asialoglycoproteins were independent of the microfilame nts, and the pH gradient in endocytic compartments was important in re ceptor-mediated endocytosis of asialgolycoproteins.