Hepatocyte water volume and potassium activity during hypotonic stress

Hepatocytes exhibit a regulatory volume decrease (RVD) during hypotonic shock, which comprises loss of intracellular K+ and Cl- accompanied by hyperpolarization of transmembrane potential (Vm) due to an increase in membrane K+ conductance, (GK). To examine hepatocyte K+ homeostasis during RVD, double-barrel, K+-selective microelectrodes were used to measure changes in steady-state intracellular K+ activity (aKi) and Vm during hyposmotic stress. Cell water volume change was evaluated by measuring changes in intracellular tetramethylammonium (TMA+). Liver slices were superfused with modified Krebs physiological salt solution. Hyposmolality (0.8 x 300 mosm) was created by a 50 mM step-decrease of external sucrose concentration. Hepatocyte Vm hyperpolarized by 19 mV from -27 +/- 1 to -46 +/- 1 mV and aiK decreased by 14% from 91 +/- 4 to 78 +/- 4 mM when slices were exposed to hyposmotic stress for 4-5 min. Both Vm and aKi returned to control level after restoring isosmotic solution. In paired measurements, hypotonic stress induced similar changes in Vm and aKi in both control and added ouabain (1 mM) conditions, and these values returned to their control level after the osmotic stress. In another paired measurement, hypotonic shock first induced an 18-mV increase in Vm and a 15% decrease in aKi in control condition. After loading hepatocytes with TMA+, the same hypotonic shock induced a 14-mV increase in Vm and a 14% decrease in aTMAi. This accounted for a 17% increase of intracellular water volume, which was identical to the cell water volume change obtained when aKi was used as the marker.(ABSTRACT TRUNCATED AT 250 WORDS)