Liu Hsin-Ping, Lin Shu-Chen, Lin Chi-Yen, Yeh Shih-Rung, Chiang Ann-Shyn
Institute of Biotechnology, National Tsing-Hua University, Hsinchu 300, Taiwan, ROC.
Insect Biochem Mol Biol. 2005 Nov;35(11):1260-8. doi: 10.1016/j.ibmb.2005.06.004. Epub 2005 Jul 27.
Juvenile hormone (JH) synthesized and released from endocrine gland corpus allatum (CA) plays an important role in insect metamorphosis, vitellogenesis and reproduction. Glutamate is a major neurotransmitter in the nervous system and its activated receptors possess excitatory and inhibitory forms in muscle fibers of invertebrates. Previously, we have shown that the rise of intracellular calcium through excitatory glutamate receptors, N-methyl-d-aspartate (NMDA) and non-NMDA-type channels stimulates JH synthesis in the cockroach, Diploptera punctata. Here, we demonstrate the occurrence of inhibitory chloride permeable glutamate (GluCl) receptors on CA cell membranes. Application of the GluCl channel activators, ibotenic acid (Ibo) and ivermectin, but not gamma-aminobutyric acid caused a decline in JH synthesis in glands of either high or low activity during the gonadotrophic cycle. Also, while recording the membrane potential of the isolated whole CA glands intracellularly, Ibo induced a hyperpolarizated response. Both changes in the membrane potential and inhibition of JH synthesis could be abolished by the application of the chloride channel blocker picrotoxin. Finally, we found both excitatory and inhibitory glutamate receptors cause antagonistic effects on rates of JH synthesis. These results indicate a novel function of GluCl channels in the inhibition of JH synthesis that could be a potential pathway for developing a new generation of insecticides.
由内分泌器官咽侧体（CA）合成并释放的保幼激素（JH）在昆虫变态、卵黄生成和繁殖过程中发挥着重要作用。谷氨酸是神经系统中的一种主要神经递质，其激活的受体在无脊椎动物的肌肉纤维中具有兴奋性和抑制性两种形式。此前，我们已经表明，通过兴奋性谷氨酸受体、N-甲基-D-天冬氨酸（NMDA）和非NMDA型通道引起的细胞内钙离子升高会刺激蟑螂双斑蟋的JH合成。在此，我们证明了CA细胞膜上存在抑制性氯离子通透型谷氨酸（GluCl）受体。应用GluCl通道激活剂鹅膏蕈氨酸（Ibo）和伊维菌素，但不应用γ-氨基丁酸，会导致在促性腺周期中高活性或低活性腺体的JH合成下降。此外，在细胞内记录分离的整个CA腺体的膜电位时，Ibo会诱导超极化反应。膜电位的变化和JH合成的抑制都可以通过应用氯离子通道阻滞剂印防己毒素来消除。最后，我们发现兴奋性和抑制性谷氨酸受体对JH合成速率都有拮抗作用。这些结果表明GluCl通道在抑制JH合成方面具有新功能，这可能是开发新一代杀虫剂的潜在途径。
