ETHANOL INCREASES HEPATOCYTE WATER VOLUME

Mouse hepatocytes respond to osmotic stress with adaptive changes in transmembrane potential, V-m, such that hypotonic stress hyperpolarizes cells and hypertonic stress depolarizes them. These changes in V-m provide 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 administered in vitro to mouse liver slices increases hepatocyte water volume, and whether this swelling triggers adaptive changes in the V-m. Cells in mouse liver slices were loaded with tetramethylammonium ion (TMA). Changes 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) increased 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 to that from untreated mice, except that the onset and peak were delayed 2 min. Hepatocyte V-m showed no differences between control or ethanol-treated cells during the course of volume changes. In contrast, hyposmotic stress, created by dropping external osmolality 50 mosm, increased Y,from -30 mV to -46 mV. Ethanol did not inhibit this osmotic stress-induced hyperpolarization, except partially at high concentrations of 257 mM or greater. We infer that ethanol-induced swelling of hepatocytes differs from that resulting from hyposmotic stress. Cellular events associated with increased activity of intracellular water most likely trigger the hyperpolarization of Y, that accompanies the latter. We conclude, therefore, that ethanol-induced swelling occurs without change in cell water activity. This may result from the retention of macromolecules by ethanol in cells that constitutively secrete protein.