ETHANOL INDUCES VESICULAR ALKALINIZATION IN RAT HEPATOCYTES

In rat hepatocytes loaded with fluorescein isothiocyanate (FITC)-dextr an, ethanol (100 mM) led to a biphasic increase of the pH of endocytot ic vesicles (control pH(ves) = 6.11 +/- 0.06, n = 77) starting with a peak (Delta pH(ves) = +0.15 +/- 0.01) followed by a sustained plateau (Delta pH(ves) = +0.09 +/- 0.02). The alkalinizing effect of ethanol w as fully reversible and was half-maximal at ethanol concentrations <5 mM. The effects of ethanol were mimicked by low concentrations (0.1 mM ) of acetaldehyde, but not by acetate or a lactate-induced shift of th e NADH/NAD(+) system to a more reduced state. Inhibition of alcohol de hydrogenase by 4-methylpyrazole (2 mM) abolished the effects of ethano l on pH(ves), but not those of acetaldehyde. The ethanol-induced pH(ve s) changes were largely abolished in the presence of colchicine, the c hloride channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, pertussis and cholera toxin and the tyrosine kinase inhibitors e rbstatin analogue and genistein. The results suggest that ethanol via acetaldehyde activates a signal transduction mechanism which triggers an alkalinization of pH(ves). This may contribute to the known effects of ethanol on the endocytotic pathway.