Martin Stéphane, Bouschet Tristan, Jenkins Emma L, Nishimune Atsushi, Henley Jeremy M
Department of Anatomy, Medical Research Council Centre for Synaptic Plasticity, University of Bristol, School of Medical Sciences, University Walk, Bristol BS8 1TD, United Kingdom.
J Biol Chem. 2008 Dec 26;283(52):36435-40. doi: 10.1074/jbc.M806447200. Epub 2008 Oct 27.
Kainate receptors (KARs) are crucial for the regulation of both excitatory and inhibitory neurotransmission, but little is known regarding the mechanisms controlling KAR surface expression. We used super ecliptic pHluorin (SEP)-tagged KAR subunit GluR6a to investigate real-time changes in KAR surface expression in hippocampal neurons. Sindbis virus-expressed SEP-GluR6 subunits efficiently co-assembled with native KAR subunits to form heteromeric receptors. Diffuse surface-expressed dendritic SEP-GluR6 is rapidly internalized following either N-methyl-d-aspartate or kainate application. Sustained kainate or transient N-methyl-d-aspartate application resulted in a slow decrease of base-line surface KAR levels. Surprisingly, however, following the initial loss of surface receptors, a short kainate application caused a long lasting increase in surface-expressed KARs to levels significantly greater than those prior to the agonist challenge. These data suggest that after initial endocytosis, transient agonist activation evokes increased KAR exocytosis and reveal that KAR surface expression is bidirectionally regulated. This process may provide a mechanism for hippocampal neurons to differentially adapt their physiological responses to changes in synaptic activation and extrasynaptic glutamate concentration.
红藻氨酸受体（KARs）对于兴奋性和抑制性神经传递的调节至关重要，但关于控制KAR表面表达的机制却知之甚少。我们使用超 ecliptic pHluorin（SEP）标记的KAR亚基GluR6a来研究海马神经元中KAR表面表达的实时变化。辛德毕斯病毒表达的SEP-GluR6亚基与天然KAR亚基有效共组装形成异聚体受体。在应用N-甲基-D-天冬氨酸或红藻氨酸后，弥漫性表面表达的树突状SEP-GluR6会迅速内化。持续应用红藻氨酸或短暂应用N-甲基-D-天冬氨酸会导致基线表面KAR水平缓慢下降。然而，令人惊讶的是，在表面受体最初丢失后，短暂应用红藻氨酸会导致表面表达的KAR持续增加，其水平显著高于激动剂刺激前的水平。这些数据表明，在最初的内吞作用后，短暂的激动剂激活会引发KAR胞吐作用增加，并揭示KAR表面表达受到双向调节。这一过程可能为海马神经元差异性地适应其对突触激活和突触外谷氨酸浓度变化的生理反应提供一种机制。
