γ1-Containing GABA-A Receptors Cluster at Synapses Where they Mediate Slower Synaptic Currents than γ2-Containing GABA-A Receptors.
γ1-Containing GABA-A Receptors Cluster at Synapses Where they Mediate Slower Synaptic Currents than γ2-Containing GABA-A Receptors.
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DOI：
10.3389/fnmol.2017.00178
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发表时间：
2017
影响因子：
4.8
通讯作者：
Durisic N
中科院分区：
文献类型：
--
作者：
Dixon CL;Sah P;Keramidas A;Lynch JW;Durisic N
GABA-A受体（GABAARs）是一种五聚体配体门控离子通道，主要由α（α1-6）、β（β1-3）和γ（γ1-3）亚基组装而成。虽然含有γ2L亚基的GABAARs介导了脑中大部分的抑制性神经传递，但γ1亚基在杏仁核、苍白球和黑质中也有显著表达。然而，这些区域中含有γ1的GABAAR的位置和功能仍不清楚。在“人工”突触中，突触后受体的亚基组成受到特异性控制，γ1掺入减缓了突触电流衰减速率，而不影响通道失活，这表明含γ1的受体不是聚集的，因此被弥散性神经递质激活。然而，我们发现，γ1受体定位于神经元突触，并在突触和突触外区域形成簇。此外，与含γ 2L的GABAAR相比，它们表现出快速的膜扩散和突触和突触周群体之间更高的交换频率。细胞内大区域的点突变和药理学分析表明，当单个非保守的γ2L残基突变为其γ1对应物（T349 L）时，突触电流衰减从γ2L-减慢到γ1-样，而不改变受体的聚集或扩散性质。此外，先前的快速灌注和单通道动力学实验显示，当在HEK 293细胞中表达时，含γ2L和γ1受体的内在关闭速率没有差异。这些观察结果与突触功能的Monte Carlo模拟一起证实了减少的聚集并不控制含γ1的GABAAR动力学。相反，他们认为，γ1和γ 2L受体表现出不同的突触电流衰减率，由于差异门控动力学定位于突触时。
GABA-A receptors (GABAARs) are pentameric ligand-gated ion channels that are assembled mainly from α (α1–6), β (β1–3) and γ (γ1–3) subunits. Although GABAARs containing γ2L subunits mediate most of the inhibitory neurotransmission in the brain, significant expression of γ1 subunits is seen in the amygdala, pallidum and substantia nigra. However, the location and function of γ1-containing GABAARs in these regions remains unclear. In “artificial” synapses, where the subunit composition of postsynaptic receptors is specifically controlled, γ1 incorporation slows the synaptic current decay rate without affecting channel deactivation, suggesting that γ1-containing receptors are not clustered and therefore activated by diffuse neurotransmitter. However, we show that γ1-containing receptors are localized at neuronal synapses and form clusters in both synaptic and extrasynaptic regions. In addition, they exhibit rapid membrane diffusion and a higher frequency of exchange between synaptic and perisynaptic populations compared to γ2L-containing GABAARs. A point mutation in the large intracellular domain and a pharmacological analysis reveal that when a single non-conserved γ2L residue is mutated to its γ1 counterpart (T349L), the synaptic current decay is slowed from γ2L- to γ1-like without changing the clustering or diffusion properties of the receptors. In addition, previous fast perfusion and single channel kinetic experiments revealed no difference in the intrinsic closing rates of γ2L- and γ1-containing receptors when expressed in HEK293 cells. These observations together with Monte Carlo simulations of synaptic function confirm that decreased clustering does not control γ1-containing GABAAR kinetics. Rather, they suggest that γ1- and γ2L-containing receptors exhibit differential synaptic current decay rates due to differential gating dynamics when localized at the synapse.