Jansen Sven, Arning Jürgen, Beyersmann Detmar
Center for Biomolecular Interactions, University of Bremen, D-28359 Bremen, Germany.
Biol Trace Elem Res. 2003 Winter;96(1-3):133-42. doi: 10.1385/BTER:96:1-3:133.
Zinc ions are essential, but at elevated concentrations, they also have toxic effects on mammalian cells. Zinc plays a crucial role in cell proliferation and differentiation and it even protects cells against apoptosis caused by various reagents. On the other hand, zinc at high concentrations causes cell death that was characterized as apoptotic by internucleosomal DNA fragmentation, formation of apoptotic bodies, and breakdown of the mitochondrial membrane potential. In the present work, a clone of rat C6 glioma cells that was resistant to toxic effects of ZnCl2 up to 250 microM was employed to study the effect of the ionophore A23187 on zinc-induced apoptosis. Neither 150 microM Zn2+ nor 100 nM A23187 alone caused apoptosis as measured by internucleosomal DNA fragmentation. However, combined exposure of C6 cells to 100 nM A23187 and 150 microM Zn2+ for 48 h was effective in inducing apoptosis. Because the so-called calcium ionophore A23187 is not specific for Ca2+ ions but also transports Zn2+ with high selectivity over Ca2+, we investigated whether this substance promoted the uptake of Zn2+ ions into C6 cells. Employing the zinc-specific fluorescence probe Zinquin, we observed that the very low concentration of 1.9 nM A23187 significantly and rapidly raised the intracellular mobile Zn2+ content. Analysis by atomic absorption spectroscopy revealed that incubation with 1.9 nM A23187 caused a doubling of the total intracellular zinc level within 60 min. We conclude that the apoptosis evoked by the combined action of Zn2+ and A23187 was the result of enhanced Zn2+ influx evoked by the ionophore, resulting in higher intracellular zinc levels.
锌离子是必不可少的，但在浓度升高时，它们对哺乳动物细胞也具有毒性作用。锌在细胞增殖和分化中起着至关重要的作用，甚至能保护细胞免受各种试剂引起的凋亡。另一方面，高浓度的锌会导致细胞死亡，其特征为核小体间DNA片段化、凋亡小体形成以及线粒体膜电位的破坏。在本研究中，使用了对高达250微摩尔ZnCl₂的毒性作用具有抗性的大鼠C6胶质瘤细胞克隆，来研究离子载体A23187对锌诱导的凋亡的影响。通过核小体间DNA片段化检测，单独的150微摩尔Zn²⁺或100纳摩尔A23187均未引起凋亡。然而，C6细胞联合暴露于100纳摩尔A23187和150微摩尔Zn²⁺ 48小时可有效诱导凋亡。由于所谓的钙离子载体A23187对Ca²⁺离子不具有特异性，而且对Zn²⁺的转运选择性高于Ca²⁺，我们研究了该物质是否促进了Zn²⁺离子进入C6细胞。使用锌特异性荧光探针锌喹，我们观察到极低浓度的1.9纳摩尔A23187能显著且迅速提高细胞内可移动Zn²⁺的含量。原子吸收光谱分析显示，与1.9纳摩尔A23187孵育60分钟内可使细胞内总锌水平加倍。我们得出结论，Zn²⁺和A23187联合作用引起的凋亡是离子载体诱发的Zn²⁺内流增强的结果，导致细胞内锌水平升高。
