EFFECT OF HYPEROSMOLARITY ON BOTH RECEPTOR-MEDIATED AND FLUID-PHASE ENDOCYTOSIS IN ETHANOL-FED ANIMALS

We have shown previously that chronic ethanol administration impairs h epatic receptor-mediated endocytosis (RME) of asialoorosomucoid (ASOR) , epidermal growth factor and insulin, whereas early uptake by fluid-p hase endocytosis (FPE) of a fluorescent dye, Lucifer Yellow (LY), is n ot altered. Results of these studies suggested that ethanol-induced in jury was primarily affecting endocytosis in coated pit areas of the pl asma membrane while internalization in noncoated membrane areas was un affected. In the present study, we investigated the effects of blockin g clathrin-coated pit mediated endocytosis by hyperosmolarity on FPE o f LY and on RME of ASOR. We also examined the effects of hyperosmolari ty on the binding and internalization of insulin, a ligand endocytosed by both RME and FPE. Uptake of LY by noncoated regions of the membran e was not altered in control animals, whereas in hepatocytes from etha nol-fed animals uptake of LY was decreased by 35-40% in the presence o f 0.12 M sucrose (P < 0.05). These hyperosmolar conditions almost comp letely inhibited (> 85%) the endocytosis of I-125-ASOR by RME in both ethanol and control cells. Results with insulin showed slight effects (20-30% impairment) on uptake of the ligand in the presence of sucrose . These results are consistent with previous reports that in normal ce lls the coated pit pathway is impaired by hyperosmolarity, whereas end ocytosis in noncoated regions is unaltered. It appears, however, that both FPE and RME in hepatocytes from ethano-fed animals are susceptibl e to perturbation by hyperosmolarity. These results indicate that the noncoated pit pathway may be sensitive to stressful conditions such as hyperosmolarity after ethanol treatment.