Ikeda Tomoko, Zhao Xilong, Kono Yoshiaki, Yeh Jay Z, Narahashi Toshio
Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, IL 60611-3008, USA.
Neurotoxicology. 2003 Dec;24(6):807-15. doi: 10.1016/S0161-813X(03)00041-X.
Fipronil is the first phenylpyrazole insecticide introduced for pest control. It is effective against some insects that have become resistant to other insecticides, and exhibits low mammalian toxicity. Although fipronil is known to block GABA receptors, the mechanisms of its selective toxicity and efficacy against insects with dieldrin-resistant GABA receptors are not fully understood. We studied the effects of fipronil on the inhibitory glutamate receptor-chloride channel complex, which is found only in invertebrates. Glutamate-activated chloride currents were recorded from neurons isolated from cockroach thoracic ganglia using the whole-cell patch clamp technique. When glutamate was applied to a neuron, it evoked inward currents with an EC50 of 36.8 +/- 3.0 microM and a Hill coefficient of 1.56 +/- 0.17. The similarity between the reversal potential and the calculated chloride equilibrium potential indicated that glutamate-induced currents were carried by chloride ions. Fipronil suppressed the glutamate-induced peak currents in a dose-dependent manner with an IC50 of 0.73 +/- 0.27 microM and a Hill coefficient of 0.68 +/- 0.15. The current decay phases were greatly prolonged after fipronil application in a concentration-dependent manner. Picrotoxinin (PTX) at 100 microM slightly suppressed glutamate-induced currents to 87.8 +/- 3.7% of the control, and dieldrin at 100 microM had no effect (96.7 +/- 3.1%). AP5 and CNQX, mammalian glutamate receptor antagonists, were without effect on glutamate-induced Cl- currents. It is concluded that the potent blocking action of fipronil against glutamate-gated chloride channels may contribute to the higher toxicity against insects than mammals, as well as the efficacy against insects resistant to other insecticides.
氟虫腈是第一种被引入用于害虫防治的苯基吡唑类杀虫剂。它对一些已对其他杀虫剂产生抗性的昆虫有效，并且对哺乳动物毒性较低。尽管已知氟虫腈会阻断GABA受体，但其选择性毒性以及对具有狄氏剂抗性GABA受体的昆虫的作用机制尚未完全清楚。我们研究了氟虫腈对仅在无脊椎动物中发现的抑制性谷氨酸受体 - 氯离子通道复合物的影响。使用全细胞膜片钳技术记录从蟑螂胸神经节分离的神经元中的谷氨酸激活的氯离子电流。当向神经元施加谷氨酸时，它会诱发内向电流，其半数有效浓度（EC50）为36.8±3.0微摩尔，希尔系数为1.56±0.17。反转电位与计算出的氯离子平衡电位之间的相似性表明，谷氨酸诱导的电流是由氯离子携带的。氟虫腈以剂量依赖性方式抑制谷氨酸诱导的峰值电流，其半数抑制浓度（IC50）为0.73±0.27微摩尔，希尔系数为0.68±0.15。在应用氟虫腈后，电流衰减阶段以浓度依赖性方式大大延长。100微摩尔的印防己毒素（PTX）略微将谷氨酸诱导的电流抑制至对照的87.8±3.7％，而100微摩尔的狄氏剂则无作用（96.7±3.1％）。哺乳动物谷氨酸受体拮抗剂AP5和CNQX对谷氨酸诱导的氯离子电流没有影响。得出的结论是，氟虫腈对谷氨酸门控氯离子通道的强效阻断作用可能导致其对昆虫的毒性高于哺乳动物，以及对其他杀虫剂耐药的昆虫具有防治效果。
