苦皮藤素Ⅳ和Ⅴ对棉铃虫幼虫神经细胞钠通道的影响

Effects of celangulin Ⅳ and Ⅴ on sodium channels in nerve cells of cotton bollworm (Helicoverpa armigera)

电压门控钠通道是神经细胞兴奋传导的基础,也是杀虫剂最主要的作用靶标。具有二氢沉香呋喃多元酯骨架的苦皮藤素Ⅳ和Ⅴ是卫矛科植物苦皮藤的主要杀虫活性成分,苦皮藤素Ⅳ和Ⅴ处理后昆虫的中毒症状分别表现为麻醉和兴奋。本实验应用全细胞膜片钳技术就苦皮藤素Ⅳ和Ⅴ对棉铃虫Helicoverpa armigera幼虫离体培养神经细胞钠离子通道的影响进行了比较。结果表明:苦皮藤素Ⅳ对TTX-敏感钠通道电流的抑制明显具有浓度和时间依赖性,高浓度(10μmol/L和1μmol/L)条件下,峰值电流迅速减小而被抑制,在较中间浓度(0.1μmol/L)时缓慢降低,而在低浓度(0.01μmol/L)下,峰值电流先增加然后再缓慢降低;苦皮藤素Ⅳ对激活电压无明显影响,但使峰值电压向正电位方向移动,在高浓度移动迅速,低浓度移动缓慢。苦皮藤素Ⅴ对TTX-敏感钠通道电流峰值有明显的增大作用,也有一定的浓度依赖性;对激活电压无明显影响,峰值电压在高浓度下变化不明显,在较低浓度(0.1μmol/L和0.01μmol/L)下向正电位方向移动明显。结果说明,苦皮藤素Ⅳ和Ⅴ可能在钠通道上有一个相同的靶标位点,但由于它们化学结构上的差异,可能对钠通道动力学的修饰不同,导致不同的生理效应,昆虫表现出不同的神经中毒症状。

As the key structure of excitability in biological systems, the voltage-gated sodium channel is targeted by a series of neurotoxins derived from plants. Celangulin Ⅳ and Ⅴ isolated from the root bark of Celastrus angulatus are the major active ingredients of the insecticidal plant which can result in reverse nerve poisoning symptoms, i.e., narcosis and excitation, respectively. Their effects on inward sodium channel current in nerve cells of cotton bollworm Helicoverpa armigera were investigated in vitro by using patch clamp technique. The results indicated that celangulin Ⅳ reduced tetrodotoxin （TTX）-sensitive inward sodium current in a concentration dependent manner. The sodium peak current was reduced immediately in high concentration （10 and 1 μmol/L）, and decreased slowly in middle concentration （0.1 μmol/L）. In low concentration （0.01 μmol/L）, however, the peak current was increased in the beginning, and then reduced. Moreover, it had no effect on activated voltage, but the peak voltage shifted to positive potential which was dependent on the concentration of celangulin Ⅳ. After treatment with celangulin Ⅴ, the TTX-sensitive inward sodium channel current was increased distinctly in a concentration dependant manner. It had no effect on activated voltage, but the peak voltage shifted to positive potential in lower concentration （0.1 and 0.01 μmol/L） of celangulin Ⅴ. Due to their chemical structure difference, celangulin Ⅳ and Ⅴ could result in qualitatively divergent kinetics of sodium channels at a shared binding site, so their physiological effects are different.