McEachern A E, Berg D K
Department of Biology, University of California, San Diego, La Jolla 92093.
Mol Pharmacol. 1988 Aug;34(2):129-35.
gamma-Aminobutyric acidA (GABAA) receptors on chick ciliary ganglion neurons can be modulated by benzodiazepines and identified by radiolabeled benzodiazepine binding. Enhancement of submaximal GABA responses by benzodiazepines was demonstrated using a multibarrel pipette to construct complete benzodiazepine dose-response curves for single cells in culture. EC50 values of 22 +/- 5 nM, 1.1 +/- 0.3 microM, and 4.6 +/- 0.5 microM were obtained for flunitrazepam, clonazepam, and chlordiazepoxide, respectively. Chlordiazepoxide shifted the GABA dose-response curve to lower GABA concentrations without increasing the maximal response to GABA, demonstrating that benzodiazepines enhance the GABA response by increasing the receptor affinity for GABA. The imidazodiazepine Ro15-1788 potentiated the GABA response with an EC50 of 250 +/- 70 nM, and Ro5-4864 (chlorodiazepam) partially blocked the GABA response both in the presence and absence of chlordiazepoxide. Scatchard analysis of data from binding studies with [3H]flunitrazepam to ganglion membrane homogenates was consistent with the presence of a single class of high affinity sites with a KD of 34 +/- 6 nM and a Bmax of 145 +/- 26 fmol/mg of protein. Several lines of evidence indicated that the sites were associated with GABAA receptors. The KD of [3H]flunitrazepam binding was similar to the EC50 for flunitrazepam modulation of the GABA response. The level of [3H]flunitrazepam binding was enhanced approximately 50% over control levels by GABA. The binding was decreased both by clonazepam and by Ro5-4864 at concentrations similar to those required for the compounds to modulate the GABA response. These studies demonstrate that ciliary ganglion GABAA receptors are similar in major respects to GABAA receptors in the central nervous system but may differ in minor pharmacological properties.
鸡睫状神经节神经元上的γ-氨基丁酸A（GABAA）受体可被苯二氮䓬调节，并可通过放射性标记的苯二氮䓬结合来鉴定。使用多管移液管为培养中的单个细胞构建完整的苯二氮䓬剂量反应曲线，证明了苯二氮䓬对亚最大GABA反应的增强作用。氟硝西泮、氯硝西泮和氯氮卓的半数有效浓度（EC50）值分别为22±5 nM、1.1±0.3 μM和4.6±0.5 μM。氯氮卓将GABA剂量反应曲线向较低的GABA浓度方向移动，而不增加对GABA的最大反应，表明苯二氮䓬通过增加受体对GABA的亲和力来增强GABA反应。咪唑并二氮䓬Ro15-1788增强GABA反应，其EC50为250±70 nM，Ro5-4864（氯地西泮）在有和没有氯氮卓的情况下均部分阻断GABA反应。用[3H]氟硝西泮对神经节膜匀浆进行结合研究的数据的Scatchard分析与存在一类KD为34±6 nM、Bmax为145±26 fmol/mg蛋白质的高亲和力位点一致。几条证据表明这些位点与GABAA受体相关。[3H]氟硝西泮结合的KD与氟硝西泮调节GABA反应的EC50相似。GABA使[3H]氟硝西泮的结合水平比对照水平提高了约50%。氯硝西泮和Ro5-4864在与化合物调节GABA反应所需浓度相似的浓度下均降低了结合。这些研究表明，睫状神经节GABAA受体在主要方面与中枢神经系统中的GABAA受体相似，但在次要药理特性上可能有所不同。
