DISRUPTION OF CELL-VOLUME REGULATION BY MERCURIC-CHLORIDE IS MEDIATEDBY 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 tr eated 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+ l oss by 0.27 mu Eq/mg protein, accounting in large part for the observe d cell swelling, The effects of mercury were blunted when hepatocytes were incubated in medium in which the Na+ was replaced with K+, and we re essentially absent when Na+ was replaced with choline(+), indicatin g an important role of Na+ influx in mediating mercury's effects on ce ll volume regulation, The inhibition of RVD by mercury was prevented i f the metal was administered as a mercaptide with dithiothreitol or gl utathione. However, when these chelating agents were added after the m ercury, only the membrane permeant dithiothreitol was able to reverse the inhibition of RVD, suggesting an intracellular site of action, Mer curic chloride also produced a concentration-dependent inhibition of t he ATP-sensitive volume-regulatory osmolyte channel in skate hepatocyt es, as assessed by inhibition of swelling-activated [C-14]taurine effl ux. [C-14]Taurine efflux was inhibited at mercury concentrations (20-4 0 mu M) that had no effect on intracellular ATP levels or ATP/ADP rati os, consistent with a direct interaction with the channel. These findi ngs indicate that mercury impairs cell volume regulation in skate hepa tocytes at multiple sites, including the volume regulatory osmolyte ch annels, and Na+ and K+ permeability pathways. The combined effects of increased Na+ influx and the inability to extrude organic osmolytes ma y account for the inhibition of RVD. (C) 1996 Academic Press, Inc.