Lee Wing-Kee, Spielmann Malte, Bork Ulrich, Thévenod Frank
Dept. of Physiology and Pathophysiology, Faculty of Medicine, University of Witten/Herdecke, D-58448 Witten, Germany.
Am J Physiol Cell Physiol. 2005 Sep;289(3):C656-64. doi: 10.1152/ajpcell.00049.2005. Epub 2005 Apr 20.
The nephrotoxic metal Cd(2+) causes mitochondrial damage and apoptosis of kidney proximal tubule cells. A K(+) cycle involving a K(+) uniporter and a K(+)/H(+) exchanger in the inner mitochondrial membrane (IMM) is thought to contribute to the maintenance of the structural and functional integrity of mitochondria. In the present study, we have investigated the effect of Cd(2+) on K(+) cycling in rat kidney cortex mitochondria. Cd(2+) (EC(50) approximately 19 microM) induced swelling of nonenergized mitochondria suspended in isotonic salt solutions according to the sequence KCl = NaCl > LiCl >> choline chloride. Cd(2+)-induced swelling of energized mitochondria had a similar EC(50) value and showed the same cation dependence but was followed by a spontaneous contraction. Mitochondrial Ca(2+) uniporter (MCU) blockers, but not permeability transition pore inhibitors, abolished swelling, suggesting the need for Cd(2+) influx through the MCU for swelling to occur. Complete loss of mitochondrial membrane potential (DeltaPsi(m)) induced by K(+) influx did not prevent contraction, but addition of the K(+)/H(+) exchanger blocker, quinine (1 mM), or the electroneutral protonophore nigericin (0.4 microM), abolished contraction, suggesting the mitochondrial pH gradient (DeltapH(m)) driving contraction. Accordingly, a quinine-sensitive partial dissipation of DeltapH(m) was coincident with the swelling-contraction phase. The data indicate that Cd(2+) enters the matrix through the MCU to activate a K(+) cycle. Initial K(+) load via a Cd(2+)-activated K(+) uniporter in the IMM causes osmotic swelling and breakdown of DeltaPsi(m) and triggers quinine-sensitive K(+)/H(+) exchange and contraction. Thus Cd(2+)-induced activation of a K(+) cycle contributes to the dissipation of the mitochondrial protonmotive force.
具有肾毒性的金属镉离子（Cd(2+)）会导致线粒体损伤以及肾近端小管细胞凋亡。一种涉及线粒体内膜（IMM）上钾离子单向转运体和钾离子/氢离子交换体的钾离子循环，被认为有助于维持线粒体的结构和功能完整性。在本研究中，我们探究了Cd(2+)对大鼠肾皮质线粒体中钾离子循环的影响。Cd(2+)（半数有效浓度（EC(50)）约为19微摩尔）会根据氯化钾 = 氯化钠 > 氯化锂 >> 氯化胆碱的顺序，诱导悬浮在等渗盐溶液中的非活性线粒体肿胀。Cd(2+)诱导的活性线粒体肿胀具有相似的EC(50)值，并表现出相同的阳离子依赖性，但随后会出现自发收缩。线粒体钙离子单向转运体（MCU）阻滞剂而非通透性转换孔抑制剂可消除肿胀，这表明肿胀的发生需要Cd(2+)通过MCU流入。钾离子流入导致的线粒体膜电位（ΔΨm）完全丧失并不能阻止收缩，但添加钾离子/氢离子交换体阻滞剂奎宁（1毫摩尔）或电中性质子载体尼日利亚菌素（0.4微摩尔）可消除收缩，这表明驱动收缩的是线粒体pH梯度（ΔpHm）。因此，ΔpHm的奎宁敏感部分耗散与肿胀 - 收缩阶段同时发生。数据表明，Cd(2+)通过MCU进入基质以激活钾离子循环。最初通过IMM中Cd(2+)激活的钾离子单向转运体进行的钾离子负载会导致渗透性肿胀和ΔΨm的破坏，并触发奎宁敏感的钾离子/氢离子交换和收缩。因此，Cd(2+)诱导的钾离子循环激活有助于线粒体质子动力的耗散。
