Tsurubuchi Yuji, Kono Yoshiaki
Institute of Agriculture and Forestry, University of Tsukuba, Tsukuba 305-8572, Japan.
Pest Manag Sci. 2003 Sep;59(9):999-1006. doi: 10.1002/ps.652.
The effects of the oxadiazine insecticide indoxacarb and its N-decarbomethoxylated metabolite (DCJW) on tetrodotoxin-resistant (TTX-R) voltage-gated sodium channels in rat dorsal ganglion neurons were studied using the whole-cell patch clamp technique. Indoxacarb and DCJW suppressed the peak amplitude of action potentials, and DCJW exhibited a faster time course and higher potency than indoxacarb in the blocking effects. In voltage-clamp experiments, indoxacarb and DCJW suppressed TTX-R sodium currents in a time-dependent manner without a steady-state level of suppression. IC50 values for indoxacarb and DCJW on TTX-R sodium currents were estimated to be 10.7 and 0.8 microM after 25 min of bath application, respectively. DCJW was about 10 times more potent than indoxacarb in blocking TTX-R sodium currents. Although the suppressive effects of indoxacarb were partially reversible after washout with drug-free external solution, no recovery of sodium current was observed in DCJW treated neurons after prolonged washout. In current-voltage relationships, both indoxacarb and DCJW blocked the sodium currents to the same degree in the entire range of membrane potentials. The sodium conductance-voltage curve was not shifted along the voltage axis by indoxacarb and DCJW at 10 microM. In contrast, the steady-state inactivation curves were shifted in the hyperpolarizing direction by indoxacarb as well as by DCJW. Based on these results, it was concluded that indoxacarb and DCJW potently blocked the TTX-R sodium channel in rat DRG neurons with hyperpolarizing shifts of the steady-state inactivation curves, suggesting preferential association of the insecticides to the inactivated state of sodium channels. The small structural variation between indoxacarb and DCJW resulted in clear differences in potency for blocking sodium channels and reversibility after washout.
采用全细胞膜片钳技术，研究了恶二嗪类杀虫剂茚虫威及其N - 脱甲氧羰基代谢物（DCJW）对大鼠背根神经节神经元中抗河豚毒素（TTX - R）电压门控钠通道的影响。茚虫威和DCJW抑制动作电位的峰值幅度，且在阻断作用方面，DCJW比茚虫威表现出更快的时间进程和更高的效力。在电压钳实验中，茚虫威和DCJW以时间依赖性方式抑制TTX - R钠电流，且不存在稳态抑制水平。在浴用25分钟后，茚虫威和DCJW对TTX - R钠电流的IC50值分别估计为10.7和0.8 microM。DCJW在阻断TTX - R钠电流方面的效力约为茚虫威的10倍。尽管用无药物的外部溶液洗脱后茚虫威的抑制作用部分可逆，但在长时间洗脱后，DCJW处理的神经元中未观察到钠电流的恢复。在电流 - 电压关系中，茚虫威和DCJW在整个膜电位范围内对钠电流的阻断程度相同。在10 microM时，茚虫威和DCJW均未使钠电导 - 电压曲线沿电压轴移动。相反，茚虫威和DCJW均使稳态失活曲线向超极化方向移动。基于这些结果，得出结论：茚虫威和DCJW有效阻断大鼠背根神经节神经元中的TTX - R钠通道，且稳态失活曲线向超极化方向移动，表明杀虫剂优先与钠通道的失活状态结合。茚虫威和DCJW之间微小的结构差异导致了阻断钠通道的效力和洗脱后可逆性的明显差异。
