EFFECTS OF MONENSIN ON ETHANOL-INDUCED ALTERATIONS IN FUNCTION OF HEPATOCELLULAR ASIALOGLYCOPROTEIN RECEPTOR SUBPOPULATIONS

Chronic ethanol consumption is associated with multiple impairments in receptor-mediated endocytosis (RME) in hepatocytes. RME mediated by t he asialoglycoprotein receptor seems to be especially impaired by etha nol. In the present study, we determined susceptibility of RME to alte rations in ethanol-fed and pair-fed control animals by the addition of a carboxylic ionophore, monensin. Monensin inhibits acidification of prelysosomal vesicular compartments, which results in a decrease in th e rate of receptor-ligand dissociation within the cell. Low levels (25 mu M) of monensin have been shown to preferentially affect receptor-l igand dissociation of one subset (state 2) of asialoglycoprotein recep tor, whereas dissociation in a second subset (state 1 receptors) seems to be relatively unaffected. We examined whether ethanol treatment pr eferentially affected one or another of these receptor subpopulations. Male Wistar rats were fed a standard ethanol-containing (36% of calor ies) or control diet for 10 to 14 weeks, and hepatocytes were prepared from the animals. Similar to previous results from our laboratory, su rface and total ligand and antibody binding were decreased by 30 to 45 % (p < 0.01) in ethanol animals, compared with controls. An ethanol-in duced impairment of receptor-ligand dissociation was also apparent in these cells, as shown by increased ratios of bound-to-free ligand duri ng continuous endocytosis. After monensin treatment, surface receptors on both ethanol and control cells showed a similar pattern of redistr ibution to the cell interior and intracellular inactivation. When kine tics of intracellular receptor-ligand dissociation were examined upon addition of monensin, the bound-to-free ligand ratios in both control and ethanol cells increased dramatically and to an equal extent. These results indicate that, in the ethanol animals, the pattern of sensiti vity to monensin is unchanged relative to controls. Thus, the relative proportion of state 1 and state 2 receptor populations do not seem to be affected after long-term feeding, and ethanol may be a perturbant that affects both state I and state 2 receptor function.