TIME-COURSE OF ETHANOL-INDUCED IMPAIRMENT IN FLUID-PHASE ENDOCYTOSIS IN ISOLATED RAT HEPATOCYTES

The time-course effects of long-term ethanol administration on fluid-p hase endocytosis were studied in isolated rat hepatocytes. Rats were p air-fed an ethanol-supplemented liquid diet or an isocaloric control d iet for 3 days, 1 wk, 2 wk or 5 wk. Hepatocytes were isolated and incu bated at 37-degrees-C with various concentrations of the fluid-phase m arker Lucifer yellow. Net internalization of the marker dye was determ ined. After as little as 1 wk, ethanol-fed rats demonstrated marked de creases in the net internalization of dye compared with pair-fed contr ols; these changes persisted throughout 5 wk of feeding. Because net i nternalization is the balance between uptake into the cells vs. efflux from the cells, these components were examined individually. Early up take was not significantly decreased by ethanol feeding; however, effl ux of preloaded Lucifer yellow from cells from the ethanol-fed animals was markedly faster than efflux from pair-fed controls. This increase d efflux was more prominent in the longer preload time (90 min) compar ed with a shorter preload time (15 min), indicating an alteration in d ye distribution among various intracellular pools. These ethanol-induc ed changes in fluid-phase endocytosis were apparent for 1 wk through 5 wk of feeding and were similar for all Lucifer yellow concentrations examined. These results indicate that the decreased net internalizatio n of Lucifer yellow through fluid-phase endocytosis is mainly a result of an ethanol-induced increase in efflux possibly caused by altered i ntracellular trafficking rather than by reduction in uptake.