The glutamate-activated anion conductance in excitatory amino acid transporters is gated independently by the individual subunits
The glutamate-activated anion conductance in excitatory amino acid transporters is gated independently by the individual subunits
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DOI：
10.1523/jneurosci.0118-07.2007
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发表时间：
2007-03-14
影响因子：
5.3
通讯作者：
Larsson, Hans Peter
中科院分区：
文献类型：
--
作者：
Koch, Hans Peter;Brown, Ronald Lane;Larsson, Hans Peter
兴奋性氨基酸转运蛋白（EAAT）使用钠和钾梯度从突触和周围的细胞外空间中清除谷氨酸，从而维持有效的突触传递并将细胞外谷氨酸浓度维持在亚神经毒性水平。除了钠驱动的谷氨酸摄取外，EAAT还通过通道样机制介导谷氨酸激活的氯离子电导。EAAT是三聚体蛋白，被认为包含三个相同的亚基。先前的研究表明，钠驱动的谷氨酸摄取独立地发生在三个亚基中的每一个中。与此相反，最近的一项研究报告高希尔系数激活EAAT阴离子电流谷氨酸，并表明，亚基的功能合作门控氯离子电导。在目前的工作中，我们发现，由谷氨酸激活的阴离子电流的希尔系数在EAAT 3和EAAT 4中都类似于1。此外，我们还使用荧光标记和EAAT3和EAAT4的失活相关性，以确定是否谷氨酸激活的氯离子电导门控独立或合作的转运。我们发现，谷氨酸摄取电流和谷氨酸激活的氯电流介导的EAAT多聚体的每个亚基独立。已经表明，具有特别大的阴离子电导的EAAT亚型可以直接影响某些神经元中突触前末梢的兴奋性。因此，发现阴离子电导门控独立，而不是合作，是很重要的，因为它显着改变预测的影响，EAAT介导的阴离子电流将在低谷氨酸浓度的突触传递。
Excitatory amino acid transporters (EAATs) use sodium and potassium gradients to remove glutamate from the synapse and surrounding extracellular space, thereby sustaining efficient synaptic transmission and maintaining extracellular glutamate concentrations at subneurotoxic levels. In addition to sodium-driven glutamate uptake, EAATs also mediate a glutamate-activated chloride conductance via a channel-like mechanism. EAATs are trimeric proteins and are thought to comprise three identical subunits. Previous studies have shown that the sodium-driven uptake of glutamate occurs independently in each of the three subunits. In contrast, a recent study reports high Hill coefficients for the activation of EAAT anion currents by glutamate and suggests that the subunits function cooperatively in gating the chloride conductance. In the present work, we find that the Hill coefficient for the activation of the anion current by glutamate is similar to 1 in both EAAT3 and EAAT4. Furthermore, we also used fluorescent labeling and inactivation correlation on EAAT3 and EAAT4 to determine whether the glutamate-activated chloride conductance is gated independently or cooperatively by the transporters. We found that both glutamate uptake currents and glutamate-activated chloride currents are mediated independently by each subunit of an EAAT multimer. It has been suggested that EAAT subtypes with particularly large anion conductances can directly influence the excitability of presynaptic terminals in certain neurons. Thus, the finding that the anion conductance is gated independently, rather than cooperatively, is important because it significantly alters predictions of the influence that EAAT-mediated anion currents will have on synaptic transmission at low glutamate concentrations.