Agonist trapping by GABAA receptor channels
Agonist trapping by GABAA receptor channels
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DOI：
10.1523/jneurosci.21-23-09083.2001
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发表时间：
2001-12-01
影响因子：
5.3
通讯作者：
Macdonald, RL
中科院分区：
文献类型：
--
作者：
Bianchi, MT;Macdonald, RL
GABA能诱导多能干细胞具有相对缓慢的衰退（失活），这似乎是由于GABA受体通道的打开，远远超过了中央突触游离GABA的预期持续时间。开放和脱敏状态被认为可以防止激动剂与受体分离，从而延长失活时间。然而，同时评估GABA结合和通道门控是不可能的。我们开发了一种GABA结合位点或位点占用的功能测定来测试GABA“捕获”假说。比较了两种情况下的失活电流，一种竞争性拮抗剂，也能变构抑制GABA(a)受体。这为GABA在门控过程中被困在受体上的假设提供了一个独立于模型的功能测试：二胡兰只有在通道开放但未被GABA结合的情况下才能抑制通道。虽然双库兰抑制自发的和神经类固醇激活的GABA(A)受体电流，但它不能改变GABA激活的GABA(A)受体电流的失活时间过程。双束线阻断对失活电流的保护表明，当通道打开时，GABA仍与受体结合，这表明所有的打开状态，以及所有可能发生通道打开的关闭和脱敏状态，都必须是GABA配体状态。诱捕可能是激动剂特有的，因为正变构调节剂地西泮与GABA(A)受体分离，独立于GABA结合和通道活性。
GABAergic IPSCs have a relatively slow decay (deactivation) that appears to result from GABA(A) receptor channel openings that occur well beyond the predicted duration of free GABA at central synapses. Open and desensitized states have been suggested to prevent dissociation of agonist from the receptor, thus prolonging deactivation. However, simultaneous assessment of GABA binding and channel gating has not been possible. We developed a functional assay for occupancy of the GABA binding site or sites to test the GABA "trapping" hypothesis. Deactivation currents were compared in the absence and presence of bicuculline, a competitive antagonist that also allosterically inhibits GABA(A) receptors. This provided a model-independent, functional test of the hypothesis that GABA is trapped on the receptor during gating: bicuculline could only inhibit the channel if it was open but unbound by GABA. Although bicuculline inhibited spontaneous and neurosteroid-activated GABA(A) receptor currents, it failed to alter the deactivation time course of GABA-activated GABA(A) receptor currents. Protection of deactivation current from bicuculline block indicated that GABA remained bound to the receptors while the channel was open, thus suggesting that all open states, as well as all closed and desensitized states from which channel opening can occur, must be GABA liganded states. Trapping may be specific to agonists, because the positive allosteric modulator diazepam unbound from GABA(A) receptors independent of GABA binding and channel activity.