Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, UK.
J Physiol. 2014 Feb 15;592(4):653-68. doi: 10.1113/jphysiol.2013.267310. Epub 2013 Dec 16.
N-Methyl-d-aspartate receptors (NMDARs) are Ca(2+)-permeable glutamate receptors that play a critical role in synaptic plasticity and promoting cell survival. However, overactive NMDARs can trigger cell death signalling pathways and have been implicated in substantia nigra pars compacta (SNc) pathology in Parkinson's disease. Calcium ion influx through NMDARs recruits Ca(2+)-dependent proteins that can regulate NMDAR activity. The surface density of NMDARs can also be regulated dynamically in response to receptor activity via Ca(2+)-independent mechanisms. We have investigated the activity-dependent regulation of NMDARs in SNc dopaminergic neurones. Repeated whole-cell agonist applications resulted in a decline in the amplitude of NMDAR currents (current run-down) that was use dependent and not readily reversible. Run-down was reduced by increasing intracellular Ca(2+) buffering or by reducing Ca(2+) influx but did not appear to be mediated by the same regulatory proteins that cause Ca(2+)-dependent run-down in hippocampal neurones. The NMDAR current run-down may be mediated in part by a Ca(2+)-independent mechanism, because intracellular dialysis with a dynamin-inhibitory peptide reduced run-down, suggesting a role for clathrin-mediated endocytosis in the regulation of the surface density of receptors. Synaptic NMDARs were also subject to current run-down during repeated low-frequency synaptic stimulation in a Ca(2+)-dependent but dynamin-independent manner. Thus, we report, for the first time, regulation of NMDARs in SNc dopaminergic neurones by changes in intracellular Ca(2+) at both synaptic and extrasynaptic sites and provide evidence for activity-dependent changes in receptor trafficking. These mechanisms may contribute to intracellular Ca(2+) homeostasis in dopaminergic neurones by limiting Ca(2+) influx through the NMDAR.
N-甲基-D-天冬氨酸受体（NMDARs）是钙（Ca 2+）通透性谷氨酸受体，在突触可塑性和促进细胞存活方面发挥着关键作用。然而，过度活跃的 NMDAR 可触发细胞死亡信号通路，并与帕金森病黑质致密部（SNc）病理学有关。NMDAR 内的钙离子流入会募集依赖 Ca 2+的蛋白，这些蛋白可以调节 NMDAR 的活性。NMDAR 的表面密度也可以通过 Ca 2+非依赖性机制对受体活性进行动态调节。我们研究了 SNc 多巴胺能神经元中 NMDAR 的活性依赖性调节。重复全细胞激动剂应用会导致 NMDAR 电流幅度下降（电流衰减），这种衰减是使用依赖性的，不易逆转。通过增加细胞内 Ca 2+缓冲或减少 Ca 2+内流可以减少衰减，但似乎不是由导致海马神经元中 Ca 2+依赖性衰减的相同调节蛋白介导的。NMDAR 电流衰减可能部分由 Ca 2+非依赖性机制介导，因为用抑制胞质分裂的肽进行细胞内透析可减少衰减，这表明网格蛋白介导的内吞作用在调节受体的表面密度方面起作用。在 Ca 2+依赖性但不依赖于胞质分裂的情况下，重复低频突触刺激也会导致突触 NMDAR 电流衰减。因此，我们首次报道了 SNc 多巴胺能神经元中 NMDAR 的调节，这种调节是由突触和细胞外部位的细胞内 Ca 2+变化引起的，并提供了与受体转运有关的活性依赖性变化的证据。这些机制可能通过限制 NMDAR 内的 Ca 2+流入来有助于多巴胺能神经元中的细胞内 Ca 2+稳态。
