Disruption of cell volume regulation by mercuric chloride is mediated by an increase in sodium permeability and inhibition of an osmolyte channel in skate hepatocytes

The mechanism by which mercury leads to cell swelling and impairs the normal regulatory volume decrease (RVD) in cells swollen in hypotonic media was examined in hepatocytes isolated from the little skate, Raja erinacea, an osmoconforming marine elasmobranch. Skate hepatocytes treated with 50 mu M HgCl2 in isotonic medium swelled to volumes double those of control cells, and this was associated with an increase in Na+ and K+ permeability, The gain in intracellular Na+ exceeded the K+ loss by 0.27 mu Eq/mg protein, accounting in large part for the observed cell swelling, The effects of mercury were blunted when hepatocytes were incubated in medium in which the Na+ was replaced with K+, and were essentially absent when Na+ was replaced with choline(+), indicating an important role of Na+ influx in mediating mercury's effects on cell volume regulation, The inhibition of RVD by mercury was prevented if the metal was administered as a mercaptide with dithiothreitol or glutathione. However, when these chelating agents were added after the mercury, only the membrane permeant dithiothreitol was able to reverse the inhibition of RVD, suggesting an intracellular site of action, Mercuric chloride also produced a concentration-dependent inhibition of the ATP-sensitive volume-regulatory osmolyte channel in skate hepatocytes, as assessed by inhibition of swelling-activated [C-14]taurine efflux. [C-14]Taurine efflux was inhibited at mercury concentrations (20-40 mu M) that had no effect on intracellular ATP levels or ATP/ADP ratios, consistent with a direct interaction with the channel. These findings indicate that mercury impairs cell volume regulation in skate hepatocytes at multiple sites, including the volume regulatory osmolyte channels, and Na+ and K+ permeability pathways. The combined effects of increased Na+ influx and the inability to extrude organic osmolytes may account for the inhibition of RVD. (C) 1996 Academic Press, Inc.