Tonically active GABAA receptors in hippocampal pyramidal neurons exhibit constitutive GABA-independent gating
Tonically active GABAA receptors in hippocampal pyramidal neurons exhibit constitutive GABA-independent gating
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DOI：
10.1124/mol.106.028597
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发表时间：
2007-02-01
影响因子：
3.6
通讯作者：
Hales, Tim G.
中科院分区：
文献类型：
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作者：
McCartney, Melissa R.;Deeb, Tarek Z.;Hales, Tim G.
海马锥体神经元的相位和强直抑制电流表现出独特的药理学特性。印防毒素和荷包牡丹碱抑制这两种成分，与 GABA(A) 受体的作用一致；然而，加巴嗪的浓度足以消除微型 GABA 能抑制性突触后电流和对外源 GABA 的反应，但对强直电流没有影响。由于锥体神经元中所有 GABA 激活的 GABA(A) 受体均对加巴嗪敏感，因此强直电流不是 GABA 激活的。此外，从外侧贴片记录的印防己毒素敏感自发单通道事件具有与 GABA 激活通道相同的弦电导，并且具有加巴嗪抗性。因此，我们假设 GABA(A) 受体在没有 GABA 的情况下持续活跃，介导强直电流；加巴嗪未能阻断强直电流反映了拮抗剂缺乏负面内在功效。我们使用全身麻醉药异丙酚直接激活锥体神经元天然的 GABA(A) 受体或在人胚胎肾 293 细胞中重组表达的 α1β3γ2 受体，比较荷包牡丹碱和加巴嗪的负面功效。当异丙酚应用于任一制剂时，都会激活耐加巴嗪、荷包牡丹碱敏感的电流。尽管加巴嗪作为丙泊酚激活电流抑制剂的功效可以忽略不计，但它阻止了荷包牡丹碱的抑制作用，而荷包牡丹碱充当抑制非 GABA 门控的反向激动剂。重组α1β1/3γ2受体还介导不依赖于激动剂的强直电流，该电流对加巴嗪具有抗性并被荷包牡丹碱抑制。因此，加巴嗪是一种竞争性拮抗剂，其负面功效可以忽略不计，因此不能抑制在缺乏 GABA 的情况下由于麻醉或自发门控而活跃的 GABA(A) 受体。此外，自发活跃的 GABA(A) 受体介导锥体神经元中的抗加巴嗪强直电流。
Phasic and tonic inhibitory currents of hippocampal pyramidal neurons exhibit distinct pharmacological properties. Picrotoxin and bicuculline methiodide inhibited both components, consistent with a role for GABA(A) receptors; however, gabazine, at a concentration that abolished miniature GABAergic inhibitory postsynaptic currents and responses to exogenous GABA, had no effect on tonic currents. Because all GABA-activated GABA(A) receptors in pyramidal neurons are gabazine- sensitive, it follows that tonic currents are not GABA- activated. Furthermore, picrotoxin- sensitive spontaneous single- channel events recorded from outside- out patches had the same chord conductance as GABA- activated channels and were gabazineresistant. Therefore, we hypothesize that GABA(A) receptors, constitutively active in the absence of GABA, mediate tonic current; the failure of gabazine to block tonic current reflects a lack of negative intrinsic efficacy of the antagonist. We compared the negative efficacies of bicuculline and gabazine using the general anesthetic propofol to directly activate GABA(A) receptors native to pyramidal neurons or alpha 1 beta 3 gamma 2 receptors recombinantly expressed in human embryonic kidney 293 cells. Propofol activated gabazine- resistant, bicuculline- sensitive currents when applied to either preparation. Although gabazine had negligible efficacy as an inhibitor of propofol- activated currents, it prevented inhibition by bicuculline, which acts as an inverse agonist inhibiting GABA- independent gating. Recombinant alpha 1 beta 1/3 gamma 2 receptors also mediated agonist- independent tonic currents that were resistant to gabazine and inhibited by bicuculline. Thus, gabazine is a competitive antagonist with negligible negative efficacy and is therefore unable to inhibit GABA(A) receptors that are active in the absence of GABA because of either anesthetic or spontaneous gating. Moreover, spontaneously active GABA(A) receptors mediate gabazine- resistant tonic currents in pyramidal neurons.