ETHANOL INCREASES HEPATOCYTE WATER VOLUME

Mouse hepatocytes respond to osmotic stress with adaptive changes in t ransmembrane potential, V-m, such that hypotonic stress hyperpolarizes cells and hypertonic stress depolarizes them. These changes in V-m pr ovide electromotive force for redistribution of ions such as Cl-, and this comprises pert of the mechanism of hepatocyte volume regulation. We conducted the present study to determine whether ethanol administer ed in vitro to mouse liver slices increases hepatocyte water volume, a nd whether this swelling triggers adaptive changes in the V-m. Cells i n mouse liver slices were loaded with tetramethylammonium ion (TMA). C hanges in hepatocyte water volume were computed from measurements with ion sensitive microelectrodes of changes in intracellular activity of TMA (a(TMA)(I)) that resulted from water fluxes. Ethanol (70 mM) incr eased hepatocyte water volume immediately, and this peaked at 17% by 7 to 8 min, by which time a plateau was reached. Liver slices also were obtained from mice treated 12 hr prior with 4-methylpyrazole (4 mM). The effect of ethanol on their hepatocyte water volume was identical t o that from untreated mice, except that the onset and peak were delaye d 2 min. Hepatocyte V-m showed no differences between control or ethan ol-treated cells during the course of volume changes. In contrast, hyp osmotic stress, created by dropping external osmolality 50 mosm, incre ased Y,from -30 mV to -46 mV. Ethanol did not inhibit this osmotic str ess-induced hyperpolarization, except partially at high concentrations of 257 mM or greater. We infer that ethanol-induced swelling of hepat ocytes differs from that resulting from hyposmotic stress. Cellular ev ents associated with increased activity of intracellular water most li kely trigger the hyperpolarization of Y, that accompanies the latter. We conclude, therefore, that ethanol-induced swelling occurs without c hange in cell water activity. This may result from the retention of ma cromolecules by ethanol in cells that constitutively secrete protein.