Glycine transporter type 1 blockade changes NMDA receptor-mediated responses and LTP in hippocampal CA1 pyramidal cells by altering extracellular glycine levels
Glycine transporter type 1 blockade changes NMDA receptor-mediated responses and LTP in hippocampal CA1 pyramidal cells by altering extracellular glycine levels
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DOI：
10.1113/jphysiol.2004.063321
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发表时间：
2004-06-01
影响因子：
5.5
通讯作者：
Bergeron, R
中科院分区：
文献类型：
--
作者：
Martina, M;Gorfinkel, Y;Bergeron, R
海马 CA1 区的长时程增强 (LTP) 需要激活 NMDA 受体 (NMDAR)。 NMDAR 激活反过来需要膜去极化以及谷氨酸及其共激动剂甘氨酸的结合。先前的药理学研究表明，1 型甘氨酸转运蛋白 (GlyT 1) 在突触 NMDAR 处维持甘氨酸的亚饱和浓度。 GlyT1 拮抗剂会增加突触间隙中甘氨酸的水平，并且与直接甘氨酸位点激动剂一样，可以增强 NMDAR 电流和 NMDAR 介导的功能，例如 LTP。此外，刺激甘氨酸位点会启动通过 NMDAR 复合物的信号传导，启动受体进行网格蛋白依赖性内吞作用。我们使用了一种新型强效 GlyT1 拮抗剂 CP-802,079，并在急性大鼠海马切片中进行全细胞膜片钳记录，以确定 GlyT 1 阻断对 LTP 的影响。在清醒、自由活动的大鼠海马体中进行的反向微透析实验表明，这种药物仅升高细胞外甘氨酸的浓度。我们发现 CP-802,079、肌氨酸和甘氨酸显着增加 NMDAR 电流和 LTP 的幅度。相反，应用较高浓度的 CP-802,079 和甘氨酸会略微降低 NMDAR 电流，但不会增加 LTP。总体而言，这些数据表明突触间隙中存在的甘氨酸水平严格调节 NMDAR 活性。由于 GlyT 1 依赖性摄取的存在，该水平保持低于 NMDAR 内化启动机制的“设定点”。
Long-term potentiation (LTP) in the hippocampal CA1 region requires the activation of NMDA receptors (NMDARs). NMDAR activation in turn requires membrane depolarization as well as the binding of glutamate and its coagonist glycine. Previous pharmacological studies suggest that the glycine transporter type 1 (GlyT 1) maintains subsaturating concentrations of glycine at synaptic NMDARs. Antagonists of GlyT1 increase levels of glycine in the synaptic cleft and, like direct glycine site agonists, can augment NMDAR currents and NMDAR-mediated functions such as LTP. In addition, stimulation of the glycine site initiates signalling through the NMDAR complex, priming the receptors for clathrin-dependent endocytosis. We have used a new potent GlyT1 antagonist, CP-802,079, with whole-cell patch-clamp recordings in acute rat hippocampal slices to determine the effect of GlyT 1 blockade on LTP. Reverse microdialysis experiments in the hippocampus of awake, freely moving rats, showed that this drug elevated only the extracellular concentration of glycine. We found that CP-802,079, sarcosine and glycine significantly increased the amplitude of the NMDAR currents and LTP. In contrast, application of higher concentrations of CP-802,079 and glycine slightly reduced NMDAR currents and did not increase LTP. Overall, these data suggest that the level of glycine present in the synaptic cleft tightly regulates the NMDAR activity. This level is kept below the 'set point' of the NMDAR internalization priming mechanism by the presence of GlyT 1-dependent uptake.