Exposure to 50 Hz electromagnetic field changes the efficiency of the scorpion alpha toxin

AbstractBackground Extremely low-frequency (50 Hz) electromagnetic field (ELF-EMF) is produced by electric power transmission lines and electronic devices of everyday use. Some phenomena are proposed as “first effects” of ELF-EMF: the discrete changes in the membrane potential and the increase of the calcium channel activity as well as the intracellular concentration of Ca 2+ . Interaction of the scorpion alpha toxin with the sodium channel depends on the orientation of the charges and may be perturbed by changes in the membrane polarization. The toxin induces overexcitability in the nervous system and an increase in the neurotransmitters released with different consequences, mainly the paralysis of muscles. We assumed that the exposure to ELF-EMF 0.7 mT will change the effects of the insect selective scorpion alpha toxin (recombinant LqhαIT from Leiurus quinquestriatus hebraeus) at the level of the cercal nerve function, the synaptic transmission and on the level of entire insect organism. Taking into account the compensatory mechanisms in organisms, we tested in addition ten times higher ELF-EMF on whole insects.Methods Experiments were performed in vivo on cockroaches (Periplaneta americana) and in vitro – on isolated cockroach abdominal nerve cord with cerci. In biotests, the effects of LqhαIT (10 −8 M) were estimated on the basis of the insect ability to turn back from dorsal to ventral side. Three groups were compared: the control one and the two exposed to ELF-EMF – 0.7 and 7 mT. Bioelectrical activity of the cercal nerve and of the connective nerve that leaves the terminal abdominal ganglion was recorded using extracellular electrodes. LqhαIT (5 × 10 −8 M) induced modifications of neuronal activity that were observed in the control cockroach preparations and in the ones exposed to ELF-EMF (0.7 mT). The exposure to ELF-EMF was carried out using coils with a size appropriate to the examined objects.Results The exposure to ELF-EMF (0.7 mT) modified the effects of LqhαIT (5 × 10−8 M) on activity of the cercal nerve and of the connective nerve. We observed a decrease of the toxin effect on the cercal nerve activity, but the toxic effect of LqhαIT on the connective nerve was increased. Biotests showed that toxicity of LqhαIT (10 −8 M) on cockroaches was reduced by the exposure to ELF-EMF (0.7 and 7 mT).Conclusions The exposure to 50 Hz ELF-EMF modified the mode of action of the anti-insect scorpion alpha toxin LqhαIT at cellular level of the cockroach nervous system and in biotests. Toxin appeared as a usefull tool in distinguishing between the primary and the secondary effects of ELF-EMF.

摘要
研究背景：极低频（50 Hz）电磁场（Extremely Low-Frequency Electromagnetic Field, ELF-EMF）由电力输电线路与日常电子设备所产生。已有研究提出ELF-EMF存在若干"初级效应"：包括膜电位的离散式变化、钙通道活性的提升，以及细胞内Ca²⁺浓度的升高。蝎源α型毒素与钠通道的相互作用依赖于电荷的空间取向，膜极化状态的改变可能会干扰这一相互作用。该毒素可引发神经系统过度兴奋，促使神经递质释放量增加，进而引发多种效应，其中以肌肉麻痹最为典型。本研究假设，暴露于0.7 mT的ELF-EMF会改变昆虫选择性蝎源α型毒素（重组自以色列金蝎Leiurus quinquestriatus hebraeus的LqhαIT）在尾须神经功能、突触传递以及整个昆虫个体层面的效应。考虑到生物体内存在代偿机制，本研究额外设置了10倍强度的ELF-EMF暴露组，在完整昆虫个体上开展实验。

实验方法：实验分为体内与体外两部分：体内实验以美洲大蠊（Periplaneta americana）为对象，体外实验则采用分离的带有尾须的美洲大蠊腹神经索。在生物测定实验中，本研究以昆虫从背侧向腹侧翻身的能力作为评价指标，来评估10⁻⁸ M浓度的LqhαIT的效应。实验共设置三组：空白对照组，以及分别暴露于0.7 mT和7 mT ELF-EMF的两个暴露组。采用细胞外电极记录尾须神经以及发自末端腹神经节的连接神经的生物电活动。在对照组美洲大蠊标本以及暴露于0.7 mT ELF-EMF的标本中，均可观察到5×10⁻⁸ M浓度的LqhαIT对神经元活动的修饰作用。ELF-EMF暴露装置采用适配实验对象尺寸的线圈搭建而成。

实验结果：暴露于0.7 mT的ELF-EMF可改变5×10⁻⁸ M浓度的LqhαIT对尾须神经及连接神经活动的效应。本研究观察到，ELF-EMF暴露使LqhαIT对尾须神经活动的效应减弱，但对连接神经的毒性效应却有所增强。生物测定实验结果显示，暴露于0.7 mT和7 mT的ELF-EMF均可降低10⁻⁸ M浓度的LqhαIT对美洲大蠊的毒性。

结论：暴露于50 Hz的ELF-EMF可在蟑螂神经系统的细胞层面以及生物测定实验中，改变抗昆虫蝎源α型毒素LqhαIT的作用模式。该毒素可作为区分ELF-EMF初级效应与次级效应的有效工具。