HEPATOCYTE WATER VOLUME AND POTASSIUM ACTIVITY DURING HYPOTONIC STRESS

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.