Burgard E C, Tietz E I, Neelands T R, Macdonald R L
Department of Neurology, University of Michigan, Ann Arbor 48104-1687, USA.
Mol Pharmacol. 1996 Jul;50(1):119-27.
The cDNAs encoding alpha 5 and gamma 2L subunit subtypes of the gamma-aminobutyric acid (GABA) type A receptor (GABAR) were transfected into L929 cells together with cDNAs encoding either the beta 1, beta 2, or beta 3 subunit subtype. Properties of expressed recombinant alpha 5 beta X gamma 2L (where X = 1,2, or 3) GABARs were studied with the use of whole-cell, patch-clamp techniques. In cells voltage-clamped at -70 mV with equlvalent bath and pipette chloride concentrations, the application of GABA produced a concentration-dependent inward chloride current with all three alpha 5 beta X gamma 2L isoforms. Minimal or no responses were recorded from cells transfected with only two subunit cDNAs, demonstrating that all three subunits were required for functional receptor assembly in these cells. The GABA concentration producing a half-maximal current was similar for beta 2 and beta 3 subtype-containing receptors (6 microM) but higher for beta 1 subtype-containing receptors (26 microM). alpha 5 beta 3 gamma 2L receptors were zinc and diazepam sensitive but zolpidem insensitive. In response to low GABA concentrations, beta 1 and beta 3 subtype-containing receptors showed outward rectification of the current-voltage relationship, whereas current-voltage responses of beta 2 subtype-containing receptors were relatively linear. Likewise, at high GABA concentrations, beta 1 and beta 3 subtype-containing receptors showed less desensitization at positive than at negative membrane potentials. Beta 2 subtype-containing receptors displayed faster desensitization at depolarized potentials. These voltage-dependent properties were characteristic of alpha 5 but not alpha 1 or alpha 6 subtype-containing receptors and were similar to responses recorded from hippocampal CA1 pyramidal neurons. Based on the pharmacological and biophysical similarities to hippocampal GABAR responses, the alpha 5 beta 3 gamma 2L isoform could represent a native GABAR subtype.
将编码γ-氨基丁酸（GABA）A型受体（GABAR）α5和γ2L亚基亚型的cDNA与编码β1、β2或β3亚基亚型的cDNA一起转染到L929细胞中。利用全细胞膜片钳技术研究了表达的重组α5βXγ2L（其中X = 1、2或3）GABAR的特性。在等效的浴液和吸管氯化物浓度下将细胞钳制在-70 mV电压时，应用GABA会使所有三种α5βXγ2L亚型产生浓度依赖性的内向氯化物电流。仅用两个亚基cDNA转染的细胞记录到最小或无反应，表明所有三个亚基都是这些细胞中功能性受体组装所必需的。产生半数最大电流的GABA浓度，含β2和β3亚型的受体相似（6μM），但含β1亚型的受体更高（26μM）。α5β3γ2L受体对锌和地西泮敏感，但对唑吡坦不敏感。响应低GABA浓度时，含β1和β3亚型的受体电流-电压关系呈外向整流，而含β2亚型的受体电流-电压响应相对呈线性。同样，在高GABA浓度下，含β1和β3亚型的受体在正膜电位下比在负膜电位下脱敏程度更低。含β2亚型的受体在去极化电位下脱敏更快。这些电压依赖性特性是含α5而非含α1或α6亚型受体的特征，并且与海马CA1锥体神经元记录到的反应相似。基于与海马GABAR反应的药理学和生物物理学相似性，α5β3γ2L亚型可能代表一种天然的GABAR亚型。
