Ballatori N, Boyer J L
Department of Environmental Medicine, University of Rochester School of Medicine, New York 14642, USA.
Toxicol Appl Pharmacol. 1996 Oct;140(2):404-10. doi: 10.1006/taap.1996.0237.
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 microM 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 microEq/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 [14C]taurine efflux. [14C]Taurine efflux was inhibited at mercury concentrations (20-40 microM) 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.
研究了汞导致细胞肿胀并损害低渗介质中肿胀细胞正常调节性容积减小（RVD）的机制，实验对象是从小斑猫鲨（Raja erinacea）分离出的肝细胞，小斑猫鲨是一种渗透压顺应性海洋软骨鱼。在等渗培养基中用50微摩尔/升氯化汞处理的鲨肝细胞肿胀至对照细胞体积的两倍，这与钠和钾通透性增加有关。细胞内钠的增加量超过钾的损失量0.27微当量/毫克蛋白质，这在很大程度上解释了观察到的细胞肿胀现象。当肝细胞在钠被钾替代的培养基中孵育时，汞的作用减弱，而当钠被胆碱替代时，汞的作用基本消失，这表明钠内流在介导汞对细胞容积调节的作用中起重要作用。如果汞与二硫苏糖醇或谷胱甘肽以硫醇盐形式给药，则可防止汞对RVD的抑制作用。然而，当这些螯合剂在汞处理后添加时，只有膜通透性的二硫苏糖醇能够逆转对RVD的抑制作用，这表明作用位点在细胞内。通过抑制肿胀激活的[14C]牛磺酸外流评估，氯化汞还对鲨肝细胞中ATP敏感性容积调节渗透剂通道产生浓度依赖性抑制作用。[14C]牛磺酸外流在汞浓度（20 - 40微摩尔/升）下受到抑制，而这些浓度对细胞内ATP水平或ATP/ADP比值没有影响，这与汞与通道的直接相互作用一致。这些发现表明，汞在多个位点损害鲨肝细胞的细胞容积调节，包括容积调节渗透剂通道以及钠和钾通透性途径。钠内流增加和无法排出有机渗透剂的综合作用可能解释了对RVD的抑制作用。
