Thio Liu Lin, Shanmugam Ananth, Isenberg Keith, Yamada Kelvin
Department of Neurology, Washington University School of Medicine, St. Louis, Missouri, USA.
J Neurophysiol. 2003 Jul;90(1):89-99. doi: 10.1152/jn.00612.2002. Epub 2003 Mar 26.
Inhibitory glycine receptors (GlyRs) in the mammalian cortex probably contribute to brain development and to maintaining tonic inhibition. Given their presence throughout the cortex, their modulation likely has important physiological consequences. Although benzodiazepines potentiate gamma-aminobutyric acidA receptors (GABAARs), they may also modulate GlyRs because binding studies initially suggested that they act at GlyRs. Furthermore, their diminished ability to potentiate neonatal GABAARs suggests that they may exert their beneficial clinical effects at another site in the developing brain. Therefore we examined the effect of benzodiazepines on whole cell currents mediated by GlyRs in cultured embryonic mouse hippocampal neurons. First, we determined the GlyR subunit composition in this preparation. Glycine, beta-alanine, and taurine activate strychnine-sensitive chloride currents in a dose-dependent manner. Maximal concentrations of the three agonists produce equal, nonadditive responses as expected of full agonists. The pharmacological properties of the GlyR currents including their pattern of modulation by picrotoxinin, picrotin, and tropisetron indicate that GlyRs consist of alpha2beta heteromers and alpha2 homomers. Reverse transcriptase polymerase chain reaction (RTPCR) studies confirmed the presence of alpha2 and beta subunits. Second, we found that micromolar concentrations of some benzodiazepines, including chlordiazepoxide and nitrazepam, inhibit GlyR currents. Nitrazepam inhibition of GlyRs is noncompetitive, is not voltage dependent, and does not reflect enhanced desensitization. Thus benzodiazepines allosterically inhibit alpha2-containing GlyRs in embryonic mouse hippocampal neurons via a "low"-affinity site.
哺乳动物皮层中的抑制性甘氨酸受体（GlyRs）可能有助于大脑发育并维持紧张性抑制。鉴于它们在整个皮层中都存在，对其进行调节可能会产生重要的生理后果。尽管苯二氮䓬类药物可增强γ-氨基丁酸A受体（GABAARs）的功能，但它们也可能调节GlyRs，因为结合研究最初表明它们作用于GlyRs。此外，它们增强新生GABAARs功能的能力减弱，这表明它们可能在发育中的大脑的另一个位点发挥有益的临床作用。因此，我们研究了苯二氮䓬类药物对培养的胚胎小鼠海马神经元中由GlyRs介导的全细胞电流的影响。首先，我们确定了该制剂中GlyR亚基的组成。甘氨酸、β-丙氨酸和牛磺酸以剂量依赖性方式激活对士的宁敏感的氯离子电流。三种激动剂的最大浓度产生相等的、非相加性反应，这是完全激动剂所预期的。GlyR电流的药理学特性，包括它们被印防己毒素、印防己苦毒素和托烷司琼调节的模式，表明GlyRs由α2β异聚体和α2同聚体组成。逆转录聚合酶链反应（RTPCR）研究证实了α2和β亚基的存在。其次，我们发现微摩尔浓度的一些苯二氮䓬类药物，包括氯氮卓和硝西泮，可抑制GlyR电流。硝西泮对GlyRs的抑制是非竞争性的，不依赖电压，也不反映脱敏增强。因此，苯二氮䓬类药物通过一个“低”亲和力位点变构抑制胚胎小鼠海马神经元中含α2的GlyRs。
