Korpi E R, Kuner T, Seeburg P H, Lüddens H
Biomedical Research Center, Alko Ltd., Helsinki, Finland.
Mol Pharmacol. 1995 Feb;47(2):283-9.
Numerous ligands affect inhibitory gamma-aminobutyric acid (GABA)A receptors, none of them showing strict receptor subtype specificity. We report here that a cerebellar GABAA receptor subtype can be uniquely modulated by furosemide but not by bumetanide, another Cl-/cation transport blocker. Furosemide specifically reversed the inhibition by GABA of t-[35S]butylbicyclophosphorothionate ([35S]TBPS) binding in the cerebellar granule cell layer, as detected by autoradiography of rat brain sections. With recombinant receptors expressed in Xenopus oocytes, furosemide antagonized potently (IC50, about 10 microM), rapidly, and reversibly GABA-evoked currents of cerebellar granule cell-specific alpha 6 beta 2 gamma 2 receptors but not alpha 1 beta 2 gamma 2 receptors (IC50, > 3 mM). Furosemide reversed GABA inhibition of [35S]TBPS binding and elevated basal [35S]TBPS binding only with alpha 6 beta 2 gamma 2 and alpha 6 beta 3 gamma 2 receptors and not with alpha 6 beta 1 gamma 2 or alpha 1 beta 1/2/3 gamma 2 receptors. It appeared to interact with the receptor complex via a novel recognition site that allosterically regulates the Cl- ionophore. Furosemide is the first subtype-selective GABAA receptor (alpha 6 beta 2/3 gamma 2) antagonist and should facilitate studies on cerebellar physiology. It might serve as a prototypic structure for the development of additional subtype-selective GABAA ligands.
众多配体可作用于抑制性γ-氨基丁酸（GABA）A受体，但无一表现出严格的受体亚型特异性。我们在此报告，一种小脑GABAA受体亚型可被速尿独特地调节，而布美他尼（另一种Cl⁻/阳离子转运阻滞剂）则不能。通过大鼠脑切片放射自显影检测发现，速尿特异性地逆转了GABA对小脑颗粒细胞层中t-[³⁵S]丁基双环磷硫酰酯（[³⁵S]TBPS）结合的抑制作用。在非洲爪蟾卵母细胞中表达的重组受体上，速尿能强效（IC50约为10 μM）、快速且可逆地拮抗小脑颗粒细胞特异性α6β2γ2受体的GABA诱发电流，但对α1β2γ2受体无此作用（IC50＞3 mM）。速尿仅对α6β2γ2和α6β3γ2受体能逆转GABA对[³⁵S]TBPS结合的抑制并提高基础[³⁵S]TBPS结合，而对α6β1γ2或α1β1/2/3γ2受体则无此作用。它似乎通过一个变构调节Cl⁻离子载体的新识别位点与受体复合物相互作用。速尿是首个亚型选择性GABAA受体（α6β2/3γ2）拮抗剂，应有助于小脑生理学研究。它可能成为开发更多亚型选择性GABAA配体的原型结构。
