Functional Properties of the Retinal Glutamate Transporters GLT-1c and EAAT5*
Functional Properties of the Retinal Glutamate Transporters GLT-1c and EAAT5*
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DOI：
10.1074/jbc.m113.517177
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发表时间：
2013-12
期刊：
影响因子：
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通讯作者：
N. Schneider;Sönke Cordeiro;Jan-Philipp Machtens;S. Braams;T. Rauen;C. Fahlke
中科院分区：
文献类型：
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作者：
N. Schneider;Sönke Cordeiro;Jan-Philipp Machtens;S. Braams;T. Rauen;C. Fahlke
背景：GLT-1c和EAAT 5是视网膜神经元共表达的两种兴奋性氨基酸转运蛋白。结果：GLT-1c和EAAT 5在谷氨酸和Na+亲和力、单个转运速率以及单位阴离子电流幅度方面存在差异。结论：GLT-1c和EAAT 5是优化的，以满足不同的生理任务。意义：确定了与GLT-1c和EAAT 5相关的单独阴离子电导相关的单一通道特性。在哺乳动物视网膜中，谷氨酸摄取由称为“兴奋性氨基酸转运蛋白（EAAT）”的谷氨酸转运蛋白家族的成员介导。在这里，我们克隆和功能特性的两个视网膜EAAT从小鼠，GLT-1/EAAT 2剪接变异体GLT-1c，和EAAT 5。EAAT是谷氨酸转运蛋白和阴离子选择性离子通道，我们使用哺乳动物细胞中的异源表达，膜片钳记录和噪声分析来研究和比较两种EAAT亚型的谷氨酸转运和阴离子通道特性。我们发现GLT-1c是一种有效的谷氨酸转运蛋白，对Na+和谷氨酸具有高亲和力，在所有测试的功能方面与原始GLT-1/EAAT 2相似。EAAT 5表现出谷氨酸转运速率太低，无法在我们的实验系统中准确测量，与GLT-1c相比，对Na+和谷氨酸的亲和力显著降低。非稳态噪声分析表明，GLT-1c和EAAT 5也不同，在相关的阴离子通道的单通道电流幅度。EAAT 5阴离子通道的单一电流幅度是GLT-1c单通道幅度的两倍。此外，在负电位下，EAAT 5阴离子通道的开放概率远大于GLT-1c。我们的数据说明了EAAT 5的独特功能特性，它是一种低亲和力和低容量的谷氨酸转运系统，具有在负电压范围内针对阴离子传导优化的阴离子通道。
Background: GLT-1c and EAAT5 are two excitatory amino acid transporters co-expressed in retinal neurons. Results: GLT-1c and EAAT5 differ in glutamate and Na+ affinity, individual transport rates as well as in unitary anion current amplitudes. Conclusion: GLT-1c and EAAT5 are optimized to fulfill different physiological tasks. Significance: Identification of unitary channel properties underlying separate anion conductances associated with GLT-1c and EAAT5. In the mammalian retina, glutamate uptake is mediated by members of a family of glutamate transporters known as “excitatory amino acid transporters (EAATs).” Here we cloned and functionally characterized two retinal EAATs from mouse, the GLT-1/EAAT2 splice variant GLT-1c, and EAAT5. EAATs are glutamate transporters and anion-selective ion channels, and we used heterologous expression in mammalian cells, patch-clamp recordings and noise analysis to study and compare glutamate transport and anion channel properties of both EAAT isoforms. We found GLT-1c to be an effective glutamate transporter with high affinity for Na+ and glutamate that resembles original GLT-1/EAAT2 in all tested functional aspects. EAAT5 exhibits glutamate transport rates too low to be accurately measured in our experimental system, with significantly lower affinities for Na+ and glutamate than GLT-1c. Non-stationary noise analysis demonstrated that GLT-1c and EAAT5 also differ in single-channel current amplitudes of associated anion channels. Unitary current amplitudes of EAAT5 anion channels turned out to be approximately twice as high as single-channel amplitudes of GLT-1c. Moreover, at negative potentials open probabilities of EAAT5 anion channels were much larger than for GLT-1c. Our data illustrate unique functional properties of EAAT5, being a low-affinity and low-capacity glutamate transport system, with an anion channel optimized for anion conduction in the negative voltage range.