Mouse hepatocyte membrane potential and chloride activity during osmotic stress

Hepatocyte transmembrane potential (Vm) during osmotic stress responds as an osmometer, in part because of changes in membrane K+ conductance. This may contribute to the electromotive force that drives transmembrane Cl- fluxes. To test this, double-barreled ion-sensitive microelectrodes were used to measure changes in steady-state intracellular Cl- activity (aiCl) during osmotic stress applied to mouse liver slices. Hyperosmotic and hyposmotic conditions were created by rapidly switching to a solution in which sucrose concentrations were increased or reduced, respectively. Hyperosmotic stress [1.4 x control osmolality (280 mosmol/kgH2O)] decreased hepatocyte Vm 46% from -39 +/- 1 to -21 +/- 1 mV (SE; n = 16 animals). Corresponding aiCl increased twofold from 19 +/- 2 to 38 +/- 3 mM. This shifted the Cl- equilibrium potential (ECl) 19 mV, from -38 +/- 0.3 to -19 +/- 2 mV. Hyposmotic stress [0.71 x control osmolality (290 mosmol/kgH2O)] increased hepatocyte Vm 64% from -28 +/- 1 to -46 +/- 1 mV (SE; n = 13 animals). Corresponding aiCl decreased 0.53-fold from 17 +/- 1 to 8 +/- 1 mM. This shifted the ECl 20 mV from -26 +/- 2 to -46 +/- 3 mV. Thus hepatocyte aiCl is in electrochemical equilibrium with Vm. The paired measurements above were repeated after addition of K(+)-channel blockers quinine or Ba2+. Ba2+ (2 mM) had no effect on either Vm or aiCl during hyperosmotic stress; however, Ba2+ significantly inhibited changes in Vm and aiCl during hyposmotic stress. Effects of quinine (0.5 mM) on Vm and aiCl during both hyperosmotic stress and hyposmotic stress were similar to those of Ba2+.(ABSTRACT TRUNCATED AT 250 WORDS)