γ-Aminobutyric acid (GABA) receptors (GABARs) are an important target for existing insecticides such as fiproles. These insecticides act as noncompetitive antagonists (channel blockers) for insect GABARs by binding to a site within the intrinsic channel of the GABAR. Recently, a novel class of insecticides, 3-benzamido-N-phenylbenzamides (BPBs), was shown to inhibit GABARs by binding to a site distinct from the site for fiproles. We examined the binding site of BPBs in the adult housefly by means of radioligand-binding and electrophysiological experiments. 3-Benzamido-N-(2,6-dimethyl-4-perfluoroisopropylphenyl)-2-fluorobenzamide (BPB 1) (the N-demethyl BPB) was a partial, but potent, inhibitor of [(3)H]4'-ethynyl-4-n-propylbicycloorthobenzoate (GABA channel blocker) binding to housefly head membranes, whereas the 3-(N-methyl)benzamido congener (the N-methyl BPB) had low or little activity. A total of 15 BPB analogs were tested for their abilities to inhibit [(3)H]BPB 1 binding to the head membranes. The N-demethyl analogs, known to be highly effective insecticides, potently inhibited the [(3)H]BPB 1 binding, but the N-methyl analogs did not even though they, too, are considered highly effective. [(3)H]BPB 1 equally bound to the head membranes from wild-type and dieldrin-resistant (rdl mutant) houseflies. GABA allosterically inhibited [(3)H]BPB 1 binding. By contrast, channel blocker-type antagonists enhanced [(3)H]BPB 1 binding to housefly head membranes by increasing the affinity of BPB 1. Antiparasitic macrolides, such as ivermectin B1a, were potent inhibitors of [(3)H]BPB 1 binding. BPB 1 inhibited GABA-induced currents in housefly GABARs expressed in Xenopus oocytes, whereas it failed to inhibit l-glutamate-induced currents in inhibitory l-glutamate receptors. Overall, these findings indicate that BPBs act at a novel allosteric site that is different from the site for channel blocker-type antagonists and that is probably overlapped with the site for macrolides in insect GABARs.

中文翻译：

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杀虫剂 3-苯甲酰氨基-N-苯基苯甲酰胺与家蝇 GABA 受体的新型变构位点以高亲和力特异性结合

γ-氨基丁酸 (GABA) 受体 (GABAR) 是现有杀虫剂（如氟虫腈）的重要靶标。这些杀虫剂通过与 GABAR 内在通道内的位点结合，充当昆虫 GABAR 的非竞争性拮抗剂（通道阻滞剂）。最近，一类新型杀虫剂 3-苯甲酰胺基-N-苯基苯甲酰胺 (BPBs) 被证明通过结合到不同于 fiproles 位点的位点来抑制 GABARs。我们通过放射性配体结合和电生理实验检查了成年家蝇中 BPB 的结合位点。3-苯甲酰胺基-N-(2,6-二甲基-4-全氟异丙基苯基)-2-氟苯甲酰胺 (BPB 1)（N-去甲基 BPB）是 [(3)H]4'- 部分但有效的抑制剂与家蝇头膜结合的乙炔基-4-n-丙基双环原苯甲酸酯（GABA 通道阻滞剂），而 3-(N-甲基) 苯甲酰胺同系物 (N-甲基 BPB) 的活性很低或很低。测试了总共 15 个 BPB 类似物抑制 [(3) H] BPB 1 与头膜结合的能力。N-去甲基类似物，已知是高效杀虫剂，有效地抑制了 [(3)H]BPB 1 结合，但 N-甲基类似物即使它们也被认为是高效的。[(3)H]BPB 1 同样与野生型和狄氏剂抗性（rdl 突变体）家蝇的头膜结合。GABA 变构抑制 [(3) H] BPB 1 结合。相比之下，通道阻滞剂型拮抗剂通过增加 BPB 1 的亲和力来增强 [(3)H]BPB 1 与家蝇头膜的结合。抗寄生虫大环内酯类药物，如伊维菌素 B1a，是 [(3)H]BPB 1 的有效抑制剂捆绑。BPB 1 抑制在非洲爪蟾卵母细胞中表达的家蝇 GABARs 中 GABA 诱导的电流，而它不能抑制抑制性 l-谷氨酸受体中 l-谷氨酸诱导的电流。总体而言，这些发现表明 BPB 作用于一个新的变构位点，该位点不同于通道阻断剂型拮抗剂的位点，并且可能与昆虫 GABAR 中大环内酯的位点重叠。