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.