Koizumi T, Yokota T, Shirakura H, Tatsumoto H, Suzuki K T
Faculty of Pharmaceutical Sciences, Chiba University, Japan.
Toxicology. 1994 Sep 6;92(1-3):115-25. doi: 10.1016/0300-483x(94)90171-6.
The present study was designed to clarify the mechanism of cadmium (Cd)-induced toxicity in rat hepatocytes. Cd and Mg-ATP induced cellular acidification at concentrations lower than 25 microM. In Mg-ATP-treated cells, maximal acidification occurred within 2.5 min, with a subsequent return to control levels. In Cd-treated cells, maximal acidification (pH 6.76) occurred 10 min after exposure to the metal, then the cytoplasmic pH began to rise but did not return to normal. Cd eliminated the membrane potential of isolated mitochondria in media at both pH 6.5 and 7.4. This effect of Cd on membrane potential was approximately equivalent in both media when the metal concentration was 5 microM, but was more intense in the medium at pH 6.5 than in the medium at pH 7.4 at the metal concentration > 5 microM. Acidic medium alone had no effect on membrane potential. Mitochondrial uptake of Cd increased in a dose-dependent manner in media at both pH 7.4 and 6.5. The uptake of 5 microM Cd was significantly increased by acidic medium, however at Cd concentrations > 5 microM, there were no pH-dependent differences in Cd uptake. The incubation of hepatocytes in the medium at pH 6.0 and 6.5 resulted in 5 and 7.5% inhibition of mitochondrial respiration in intact cells, respectively. The presence of 10 microM Cd in the medium at pH 6.0 enhanced this inhibition. Mitochondrial respiration was inhibited to 60% of the control mitochondria at pH 7.4 when exposed to the medium at pH 6.5 without Cd and this inhibition was extended to 70% by the presence of 5 microM Cd. Cd in the medium at pH 7.4 had no deleterious effect on mitochondrial respiration at all concentrations examined. The results indicate that the respiratory activity of mitochondria is sensitive to the low pH rather than to Cd although the metal strongly inhibits the activity when in the medium at low pH. Therefore, it appears Cd-induced acidification plays an important role in the initiation of deteriorative processes in mitochondria.
本研究旨在阐明镉（Cd）诱导大鼠肝细胞毒性的机制。Cd和Mg-ATP在浓度低于25 microM时可诱导细胞酸化。在Mg-ATP处理的细胞中，最大酸化在2.5分钟内发生，随后恢复到对照水平。在Cd处理的细胞中，暴露于金属10分钟后出现最大酸化（pH 6.76），然后细胞质pH开始上升但未恢复正常。Cd消除了pH 6.5和7.4的培养基中分离线粒体的膜电位。当金属浓度为5 microM时，Cd对膜电位的这种影响在两种培养基中大致相同，但当金属浓度> 5 microM时，在pH 6.5的培养基中比在pH 7.4的培养基中更强烈。单独的酸性培养基对膜电位没有影响。在pH 7.4和6.5的培养基中，线粒体对Cd的摄取呈剂量依赖性增加。5 microM Cd的摄取在酸性培养基中显著增加，然而当Cd浓度> 5 microM时，Cd摄取没有pH依赖性差异。在pH 6.0和6.5的培养基中孵育肝细胞分别导致完整细胞中线粒体呼吸抑制5%和7.5%。在pH 6.0的培养基中存在10 microM Cd增强了这种抑制作用。当暴露于不含Cd的pH 6.5的培养基时，pH 7.4的线粒体呼吸被抑制至对照线粒体的60%，并且通过存在5 microM Cd这种抑制作用扩展至70%。在pH 7.4的培养基中，在所检测的所有浓度下Cd对线粒体呼吸均无有害影响。结果表明，线粒体的呼吸活性对低pH敏感而非对Cd敏感，尽管金属在低pH培养基中强烈抑制该活性。因此，似乎Cd诱导的酸化在启动线粒体的恶化过程中起重要作用。
