Characterization of a swelling-activated anion conductance in homozygous typing cell hepatoma cells

Liver cell volume and intracellular ion concentrations are maintained within a narrow physiologic range by regulated changes in membrane ion permeability. These studies of homozygous HTC hepatoma cells, a model liver cell line, evaluate the relationship between cell volume and membrane ion permeability, and assess the possibility that cell swelling allows the efflux of the intracellular osmolite taurine through the opening of a conductive pathway. Cell swelling induced by exposure to hypotonic solutions (203 mOsm) caused a rapid increase in cell volume, followed by recovery toward basal values. Volume recovery was inhibited by Cl^- depletion or by exposure to the putative Cl^- channel blocker 5-nitro-2-(3-phenylpropyl-amino) benzoic acid (NPPB) (25 μmol/L). Swelling increased the efflux rates of ³⁶Cl (181% ± 15%, P < .01) and ¹²⁵I (310% ± 21%, P < .01). In whole cell patch clamp recordings, cell swelling induced by 1) exposure to hypotonic solution or 2) intracellular perfusion with hypertonic sucrose-containing solutions activated an anion-selective current which was outwardly rectified and showed time-dependent inactivation at depolarizing potentials. The current density at -80 mV increased proportionally with increases in the transmembrane osmotic gradient from basal values of -1 pA/pF to maximal values of 70 pA/pF with 100 mmol/L sucrose in the pipette. Basal taurine permeability was low, but cell swelling increased the efflux of [1,2-³H]taurine to 1,587% ± 172% of basal levels (P < .05). Intracellular perfusion with hypertonic solutions activated currents carried by anionic taurine, with an estimated taurine/Cl^- permeability ratio of .88 ± .17 for whole cell currents. These studies demonstrate that the HTC membrane anion permeability is closely coupled to changes in cell volume, and that the recovery from swelling depends upon activation of anion-selective conductance pathways permeable to both Cl^- and taurine.