School of Life Sciences, University of Technology Sydney, Broadway, NSW 2007, Australia.
Institute for Molecular Bioscience, University of Queensland, Brisbane St. Lucia, QLD 4072, Australia; School of Pharmacy, University of Queensland, Brisbane St. Lucia, QLD 4072, Australia.
Neuropharmacology. 2017 Dec;127:224-242. doi: 10.1016/j.neuropharm.2017.04.008. Epub 2017 Apr 8.
κ-Hexatoxins (κ-HXTXs) are a family of excitotoxic insect-selective neurotoxins from Australian funnel-web spiders that are lethal to a wide range of insects, but display no toxicity towards vertebrates. The prototypic κ-HXTX-Hv1c selectively blocks native and expressed cockroach large-conductance calcium-activated potassium (BK or K1.1) channels, but not their mammalian orthologs. Despite this potent and selective action on insect K1.1 channels, we found that the classical K1.1 blockers paxilline, charybdotoxin and iberiotoxin, which all block insect K1.1 channels, are not lethal in crickets. We therefore used whole-cell patch-clamp analysis of cockroach dorsal unpaired median (DUM) neurons to study the effects of κ-HXTX-Hv1c on sodium-activated (K), delayed-rectifier (K) and 'A-type' transient (K) K channels. 1 μM κ-HXTX-Hv1c failed to significantly inhibit cockroach K and K channels, but did cause a 30 ± 7% saturating inhibition of K channel currents, possibly via a Kv4 (Shal-like) action. However, this modest action at such a high concentration of κ-HXTX-Hv1c would indicate a different lethal target. Accordingly, we assessed the actions of κ-HXTX-Hv1c on neurotransmitter-gated ion channels in cockroach DUM neurons. We found that κ-HXTX-Hv1c failed to produce any major effects on GABA or glutamate-Cl receptors but dramatically slowed nicotine-evoked ACh receptor (nAChR) current decay and reversed nAChR desensitization. These actions occurred without any alterations to nAChR current amplitude or the nicotine concentration-response curve, and are consistent with a positive allosteric modulation of nAChRs. κ-HXTX-Hv1c therefore represents the first venom peptide that selectively modulates insect nAChRs with a mode of action similar to the excitotoxic insecticide spinosyn A. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'
κ-六毒素（κ-HXTXs）是一类来自澳大利亚漏斗网蜘蛛的致昆虫神经毒素，对广泛的昆虫具有致死性，但对脊椎动物没有毒性。原型κ-HXTX-Hv1c 选择性地阻断天然和表达的蟑螂大电导钙激活钾（BK 或 K1.1）通道，但不阻断其哺乳动物同源物。尽管对昆虫 K1.1 通道具有这种强大和选择性的作用，但我们发现，经典的 K1.1 阻断剂紫杉碱、蛛毒素和 Iberiotoxin，这些阻断剂都阻断昆虫 K1.1 通道，在蟋蟀中却没有致死作用。因此，我们使用蟑螂背侧非配对中神经（DUM）神经元的全细胞膜片钳分析来研究 κ-HXTX-Hv1c 对钠激活（K）、延迟整流（K）和 'A 型' 瞬态（K）K 通道的影响。1 μM 的 κ-HXTX-Hv1c 未能显著抑制蟑螂 K 和 K 通道，但确实导致 K 通道电流产生 30±7%的饱和抑制，可能通过 Kv4（Shal 样）作用。然而，κ-HXTX-Hv1c 在如此高浓度下的这种适度作用表明存在不同的致死靶标。因此，我们评估了 κ-HXTX-Hv1c 在蟑螂 DUM 神经元中对神经递质门控离子通道的作用。我们发现，κ-HXTX-Hv1c 对 GABA 或谷氨酸-Cl 受体没有产生任何重大影响，但显著减缓了尼古丁诱导的 ACh 受体（nAChR）电流衰减并逆转了 nAChR 脱敏。这些作用发生时，nAChR 电流幅度或尼古丁浓度-反应曲线没有任何改变，与 nAChR 的正变构调节一致。κ-HXTX-Hv1c 因此代表了第一种选择性调节昆虫 nAChR 的毒液肽，其作用模式类似于致昆虫毒剂 Spinosyn A。本文是题为“毒液衍生肽作为药理学工具”的特刊的一部分。
