Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PE C1A4P3, Canada.
Aquat Toxicol. 2010 Mar 1;96(4):319-27. doi: 10.1016/j.aquatox.2009.11.019. Epub 2009 Dec 1.
The interactive effects of cadmium (Cd) and calcium (Ca) on energy metabolism in rainbow trout liver mitochondria were studied to test the prediction that Ca would protect against Cd-induced mitochondrial liability. Isolated rainbow trout liver mitochondria were energized with malate and glutamate and exposed to increasing concentrations (5-100 microM) of Cd and Ca singly and in combination at 15 degrees C. Accumulation of Cd and Ca in the mitochondria and mitochondrial respiration (oxygen consumption) rates were measured. Additionally, un-energized mitochondria were incubated with low doses (1 microM) of Cd and Ca singly and in combination, with time-course measurements of cation accumulation/binding and oxygen consumption rates. In energized actively phosphorylating mitochondria, the uptake rates of both Cd and Ca were dose-dependent and enhanced when administered concurrently. Upon low-dose incubation, Cd accumulation was rapid and peaked in 5 min, while no appreciable uptake of Ca occurred. Functionally, the resting (state 4, ADP-limited) respiration rate was not affected in the dose-response exposure, but it decreased remarkably on low-dose incubation. Adenosine diphosphate (ADP)-stimulated respiration (state 3) rate was impaired dose-dependently with maximal inhibitions (at the highest dose, 100 microM) of 32, 64 and 73% for Ca, Cd, and combined exposures, respectively. The combined effects of Ca and Cd suggested synergistic (more than additive) action and partial additivity of effects at low and higher doses of the two cations, respectively. Moreover, on a molar basis, Cd was twice as toxic as Ca to rainbow trout liver mitochondria and when combined, approximately 90% of the effects were attributable to Cd. The coupling efficiency, as measured by respiratory control ratio (RCR) and phosphorylation efficiency, measured as ADP/O ratio, both decreased as the exposure dosage and duration increased. In addition, Cd and Ca exposure decreased mitochondrial proton leak (state 4+ respiration) rates on prolonged exposure possibly by inhibiting processes that generate mitochondrial membrane potential, the force that drives proton leak. Overall these data suggest that the widely accepted theme that Ca and Cd are competitive antagonists does not hold for mitochondrial effects and that Cd and Ca cooperate to impair oxidative phosphorylation in rainbow trout liver mitochondria.
研究了镉（Cd）和钙（Ca）对虹鳟鱼肝线粒体能量代谢的交互作用，以检验 Ca 会保护线粒体免受 Cd 诱导的损伤的预测。用苹果酸和谷氨酸将分离的虹鳟鱼肝线粒体供能，并在 15°C 下单独和组合地暴露于逐渐增加的浓度（5-100μM）的 Cd 和 Ca 中。测量了线粒体中 Cd 和 Ca 的积累以及线粒体呼吸（耗氧量）率。此外，用低剂量（1μM）的 Cd 和 Ca 单独和组合孵育未供能的线粒体，并进行阳离子积累/结合和耗氧量的时间过程测量。在受激主动磷酸化的线粒体中，Cd 和 Ca 的摄取率均呈剂量依赖性，并且当同时给药时增强。在低剂量孵育时，Cd 的积累迅速，在 5 分钟时达到峰值，而 Ca 的吸收则微不足道。在功能上，在剂量反应暴露中，静息（状态 4，ADP 限制）呼吸率不受影响，但在低剂量孵育时显着下降。ADP 刺激的呼吸（状态 3）率呈剂量依赖性下降，最大抑制率（在最高剂量 100μM 时）分别为 Ca、Cd 和联合暴露的 32%、64%和 73%。Ca 和 Cd 的联合作用表明，两种阳离子的低剂量和高剂量分别具有协同（大于相加）作用和部分相加作用。此外，按摩尔计，Cd 对虹鳟鱼肝线粒体的毒性是 Ca 的两倍，当联合使用时，约 90%的作用归因于 Cd。作为呼吸控制比（RCR）和磷酸化效率（ADP/O 比）测量的耦合效率均随着暴露剂量和时间的增加而降低。此外，Cd 和 Ca 暴露会随着时间的延长降低线粒体质子泄漏（状态 4+呼吸）率，这可能是通过抑制产生线粒体膜电位的过程来实现的，而线粒体膜电位是驱动质子泄漏的力。总的来说，这些数据表明，广泛接受的 Ca 和 Cd 是竞争性拮抗剂的主题不适用于线粒体效应，并且 Cd 和 Ca 合作损害虹鳟鱼肝线粒体的氧化磷酸化。
