Department of Physiology, Development & Neuroscience, University of Cambridge, UK.
Graduate College of Biomedical Sciences, Western University of Health Sciences, USA.
Neuropharmacology. 2018 Jul 15;137:221-229. doi: 10.1016/j.neuropharm.2018.05.003. Epub 2018 May 4.
Repeated activation of N-Methyl-d-aspartate receptors (NMDARs) causes a Ca-dependent reduction in NMDAR-mediated current in dopamine (DA) neurons of the substantia nigra pars compacta (SNc) in one week old rats; however, a Ca-dependent regulatory protein has not been identified. The role of the Ca-dependent cysteine protease, calpain, in mediating NMDAR current rundown was investigated. In brain slices from rats aged postnatal day 7-9 ('P7'), bath application of either of the membrane permeable calpain inhibitors, N-Acetyl-L-leucyl-L-leucyl-L-norleucinal (ALLN, 20 μM) or MDL-28170 (30 μM) significantly reduced whole-cell NMDAR current rundown. To investigate the role of the calpain-2 isoform, the membrane permeable calpain-2 inhibitor, Z-Leu-Abu-CONH-CH2-C6H3 (3, 5-(OMe)2 (C2I, 200 nM), was applied; C2I application significantly reduced whole cell NMDAR current rundown. Interestingly, ALLN but not C2I significantly reduced rundown of NMDA-EPSCs. These results suggest the calpain-2 isoform mediates Ca-dependent regulation of extrasynaptic NMDAR current in the first postnatal week, while calpain-1 might mediate rundown of synaptic NMDAR currents. One week later in postnatal development, at P12-P16 ('P14'), there was significantly less rundown in SNc-DA neurons, and no significant effect on rundown of either Ca chelation or treatment with the calpain inhibitor, ALLN, suggesting that the rundown observed in SNc-DA neurons from two week-old rats might be Ca-independent. In conclusion, Ca-dependent rundown of extrasynaptic NMDAR currents in SNc DA neurons involves calpain-2 activation, but Ca- and calpain-2-dependent NMDAR current rundown is developmentally regulated.
反复激活 N-甲基-D-天冬氨酸受体 (NMDAR) 会导致在一周龄大鼠黑质致密部 (SNc) 的多巴胺 (DA) 神经元中 NMDAR 介导的电流产生 Ca 依赖性减少；然而，尚未鉴定出 Ca 依赖性调节蛋白。研究了 Ca 依赖性半胱氨酸蛋白酶钙蛋白酶在介导 NMDAR 电流耗竭中的作用。在来自年龄为出生后 7-9 天（'P7'）的大鼠的脑片中，在浴液中应用膜透性钙蛋白酶抑制剂 N-乙酰-L-亮氨酰-L-亮氨酰-L-正亮氨酸（ALLN，20 μM）或 MDL-28170（30 μM）均可显著减少全细胞 NMDAR 电流耗竭。为了研究钙蛋白酶-2 同工型的作用，应用了膜透性钙蛋白酶-2 抑制剂 Z-Leu-Abu-CONH-CH2-C6H3（3,5-(OMe)2（C2I，200 nM）；C2I 的应用显著减少了全细胞 NMDAR 电流耗竭。有趣的是，ALLN 但不是 C2I 显著减少了 NMDA-EPSC 的耗竭。这些结果表明，钙蛋白酶-2 同工型介导了出生后第一周 extrasynaptic NMDAR 电流的 Ca 依赖性调节，而钙蛋白酶-1 可能介导了突触 NMDAR 电流的耗竭。在出生后发育的一周后，即 P12-P16（'P14'），SNc-DA 神经元中的耗竭明显减少，而对 Ca 螯合或钙蛋白酶抑制剂 ALLN 的处理没有显著影响，这表明从两周龄大鼠的 SNc-DA 神经元中观察到的耗竭可能是 Ca 非依赖性的。总之，SNc DA 神经元中 extrasynaptic NMDAR 电流的 Ca 依赖性耗竭涉及钙蛋白酶-2 的激活，但 Ca 和钙蛋白酶-2 依赖性 NMDAR 电流耗竭受到发育调节。
