The Apparent Voltage Dependence of GABAA Receptor Activation and Modulation Is Inversely Related to Channel Open Probability
The Apparent Voltage Dependence of GABAA Receptor Activation and Modulation Is Inversely Related to Channel Open Probability
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DOI：
10.1124/mol.111.074476
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发表时间：
2012-02-01
影响因子：
3.6
通讯作者：
Jenkins, Andrew
中科院分区：
文献类型：
--
作者：
O'Toole, Kate K.;Jenkins, Andrew
GABA A 型受体 (GABA(A)R) 在整个大脑中普遍表达，是许多治疗药物的靶标，包括全身麻醉药和苯二氮卓类药物，它们通过增加离子通道的开放概率 (P-o) 来增强受体功能。受体药理学特征的体外研究通常使用负膜保持电位来模拟神经元的静息电位，并使用对称氯离子来消除戈德曼整流，与体内条件相比，这会导致氯离子沿相反方向流动。这种关键差异通常被忽视，因为据报道 GABA(A)R 表现为欧姆孔，但我们的结果表明电流-电压关系相对于 P-o 是非线性的。具体来说，我们发现电流在低 P-o 时向外整流，在高 P-o 时呈线性。我们用部分激动剂哌啶-4-磺酸和门控受损突变α1(L277A)证实了P-o和整流之间的相关性；两者都表现出增强的向外整流。此外，这种相关性与高盛整流无关，并且在改变的氯离子梯度条件下持续存在，这表明整流与氯离子通量的方向相关。最后，我们的结果表明，全身麻醉药（依托咪酯、丙泊酚和异氟烷）在负膜电位下的增强程度更大。因此，传统的体外实验高估了 GABA(A)R 正变构调节剂的作用。我们的结果表明，为了全面了解药物对配体门控离子通道的作用，必须同时考虑渗透离子驱动力的方向以及 P-o。
The GABA type A receptor (GABA(A)R) is expressed ubiquitously throughout the brain and is a target for many therapeutic agents, including general anesthetics and benzodiazepines, which enhance receptor function by increasing the open probability (P-o) of the ion channel. It is commonplace for in vitro studies of receptor pharmacological characteristics to use negative membrane holding potentials to mimic the resting potential of neurons and symmetrical chloride to eliminate Goldman rectification, which results in chloride flow in the opposite direction, compared with in vivo conditions. This critical difference is usually overlooked because the GABA(A)R has been reported to behave as an ohmic pore, but our results show that the current-voltage relationship is nonlinear with respect to P-o. Specifically, we found that currents were outwardly rectifying at low P-o and linear at high P-o. We confirmed the correlation between P-o and rectification with a partial agonist, piperidine-4-sulfonic acid, and a gating-impaired mutation, alpha 1(L277A); both exhibited enhanced outward rectification. Furthermore, this correlation was independent of Goldman rectification and persisted under altered chloride gradient conditions, which suggests that rectification is linked to the direction of chloride flux. Finally, our results showed that the degree of potentiation by general anesthetics (etomidate, propofol, and isoflurane) was greater at negative membrane potentials. Traditional in vitro experiments thus overestimate the action of positive allosteric modulators of the GABA(A)R. Our results show that the direction of the driving force on the permeant ion, as well as P-o, must be considered together for a complete understanding of drug actions on ligand-gated ion channels.