Shafer T J
Neurotoxicology Division, National Health and Environmental Effects Research Laboratory, US Environmental Protection Agency, Research Triangle Park, NC 27711, USA.
Toxicol Lett. 1998 Nov 12;99(3):207-21. doi: 10.1016/s0378-4274(98)00225-2.
Effects of the neurotoxic heavy metals Cd2+, Pb2+ and CH3Hg+ on current carried by Ca2+ ions (I(Ca)) through high-voltage activated Ca2+ channels in nerve growth factor (NGF)-differentiated pheochromocytoma (PC12) cells were examined to characterize possible differences in the mechanism of action of these metals on Ca2+ channel function. Specifically, the potency and reversibility of effect on I(Ca) by each metal was examined, as well as the relationship between extracellular [Ca2+] and potency of block of I(Ca) by Cd2+ and Pb2+. In addition, the effect of each of these metals on Ca2+ channels when applied to the intracellular side of the membrane was also examined. When extracellular solution contained 20, 10 or 5 mM Ca2+, the estimated IC50 values (total metal concentration) for block of I(Ca) were 15, 10, and 6.5 microM for Cd2+ and 7.5, 2.0 and 1.1 microM for Pb2+, respectively. CH3Hg+ (1-10 microM) blocked I(Ca) (20 mM Ca2+) in a time- and concentration-dependent manner. When cells were washed with metal-free solutions, block of I(Ca) by Cd2+ was reversed rapidly, whereas block by Pb2+ was reversed only partially, and block of I(Ca) by CH3Hg+ was not reversed. When Pb2+ and CH3Hg+ treated cells were washed in metal-free solutions containing 50 microM D-penicillamine (DPEN), block of I(Ca) by 10 microM Pb2+ was rapidly and completely reversed, whereas, block of I(Ca) by 5 microM CH3Hg+ was not reversed. Higher concentrations (500 microM) of 2,3-dimercapto-1-propane sulfonic acid (DMPS) did reverse partially the block of I(Ca) by 5 and 10 microM CH3Hg+. When Cd2+, Pb2+ or CH3Hg+ was present in the intracellular solution, Ca2+ channel currents were significantly reduced. These results characterize effects of Cd2+ on Ca2+ channels and demonstrate that Cd2+, Pb2+ and CH3Hg+ differ in their actions on Ca2+ channels.
研究了神经毒性重金属Cd2+、Pb2+和CH3Hg+对神经生长因子（NGF）分化的嗜铬细胞瘤（PC12）细胞中通过高压激活Ca2+通道的Ca2+离子电流（I(Ca)）的影响，以表征这些金属对Ca2+通道功能作用机制的可能差异。具体而言，研究了每种金属对I(Ca)影响的效力和可逆性，以及细胞外[Ca2+]与Cd2+和Pb2+对I(Ca)阻断效力之间的关系。此外，还研究了将这些金属应用于细胞膜内侧时对Ca2+通道的影响。当细胞外溶液含有20、10或5 mM Ca2+时，Cd2+阻断I(Ca)的估计IC50值（总金属浓度）分别为15、10和6.5 microM，Pb2+分别为7.5、2.0和1.1 microM。CH3Hg+（1-10 microM）以时间和浓度依赖性方式阻断I(Ca)（20 mM Ca2+）。当用无金属溶液洗涤细胞时，Cd2+对I(Ca)的阻断迅速逆转，而Pb2+对I(Ca)的阻断仅部分逆转，CH3Hg+对I(Ca)的阻断未逆转。当用含50 microM D-青霉胺（DPEN）的无金属溶液洗涤经Pb2+和CH3Hg+处理的细胞时，10 microM Pb2+对I(Ca)的阻断迅速且完全逆转，而5 microM CH3Hg+对I(Ca)的阻断未逆转。较高浓度（500 microM）的2,3-二巯基-1-丙烷磺酸（DMPS）确实部分逆转了5和10 microM CH3Hg+对I(Ca)的阻断。当细胞内溶液中存在Cd2+、Pb2+或CH3Hg+时，Ca2+通道电流显著降低。这些结果表征了Cd2+对Ca2+通道的影响，并证明Cd2+、Pb2+和CH3Hg+对Ca2+通道的作用不同。
