K. Wang et R. Wondergem, HEPATOCYTE WATER VOLUME AND POTASSIUM ACTIVITY DURING HYPOTONIC STRESS, The Journal of membrane biology, 135(2), 1993, pp. 137-144
Hepatocytes exhibit a regulatory volume decrease (RVD) during hypotoni
c shock, which comprises loss of intracellular K+ and Cl- accompanied
by hyperpolarization of transmembrane potential (V(m)) due to an incre
ase in membrane K+ conductance, (G(K)). To examine hepatocyte K+ homeo
stasis during RVD, double-barrel, K+-selective microelectrodes were us
ed to measure changes in steady-state intracellular K+ activity (a(K)i
and V(m) during hyposmotic stress. Cell water volume change was evalu
ated by measuring changes in intracellular tetramethylammonium (TMA+).
Liver slices were superfused with modified Krebs physiological salt s
olution. Hyposmolality (0.8 x 300 mosm) was created by a 50 mm step-de
crease of external sucrose concentration. Hepatocyte V(m) hyperpolariz
ed by 19 mV from - 27 +/- 1 to -46 +/- 1 mV and a(K)i decreased by 14%
from 91 +/- 4 to 78 +/- 4 mm when slices were exposed to hyposmotic s
tress for 4-5 min. Both V(m) and a(K)i returned to control level after
restoring isosmotic solution. In paired measurements, hypotonic stres
s induced similar changes in V(m) and a(K)i in both control and added
ouabain (I mm) conditions, and these values returned to their control
level after the osmotic stress. In another paired measurement, hypoton
ic shock first induced an 18-mV increase in V(m) and a 15% decrease in
a(K)i in control condition. After loading hepatocytes with TMA+, the
same hypotonic shock induced a 14-mV increase in V(m) and a 14% decrea
se in a(TMA)i. This accounted for a 17% increase of intracellular wate
r volume, which was identical to the cell water volume change obtained
when a(K)i was used as the marker. Nonetheless, hyposmotic stress-ind
uced changes in V(m) and a)K)i were blocked partly by Ba2+ (2 mm). We
conclude that (i) hepatocyte V(m) increases and a(K)i decreases during
hypotonic shock; (ii) the changes in hepatocyte V(m) and a(K)i during
and after hypotonic shock are independent of the Na+-K+ pump; (iii) t
he decrease in a(K)i during hypotonic stress results principally from
hepatocyte swelling.