Ravi J. Sharma

A differential effect between the acute and chronic administration of ethanol on the endocytotic rate konstant, ke, for internalisation of asialoglycoproteins by hepatocytes

The endocytotic rate constant, ke, originally described for the quantification of epidermal growth factor by fibroblasts (Wiley, H.S. and Cunningham, D.D. (1982) J. Biol. Chem. 257, 4222-4229) has been adapted to measure receptor-mediated endocytosis of asialoglycoproteins by hepatocytes. A ke value of 0.21 min-1 was obtained for the internalisation of beta-D-galactosyl bovine serum albumin by freshly isolated hepatocytes. The addition of ethanol to the incubation medium had a biphasic effect on ke. The value of ke was increased by up to 30% by low concentrations of ethanol, whereas higher concentrations progressively decreased ke and in 500 mM ethanol the ke value was 0.1 min-1. The amount of ligand bound to the cell surface was independent of the extracellular concentration of ethanol and the changes in ke were exclusively due to changes in the amount of internalised ligand. There was a progressive decrease in the value of ke in hepatocytes prepared from rats that were maintained on an ethanol-impregnated liquid diet for up to 20 days. The decrease was already apparent by day 2 when blood alcohol levels were only 50 mg%, indicating that the effect of chronic alcoholism on endocytosis are manifested at an early stage.