Shah Mala M, Haylett Dennis G
Department of Pharmacology, University College London, London WC1E 6BT, United Kingdom.
J Neurophysiol. 2002 Jun;87(6):2983-9. doi: 10.1152/jn.2002.87.6.2983.
Long lasting outward currents mediated by Ca2+-activated K+ channels can be induced by Ca2+ influx through N-methyl-D-aspartate (NMDA)-receptor channels in voltage-clamped hippocampal pyramidal neurons. Using specific inhibitors, we have attempted to identify the channels that underlie these outward currents. At a holding potential of -50 mV, applications of 1 mM NMDA to the soma of cultured hippocampal pyramidal neurons induced the expected inward currents. In 44% of cells tested, these were followed by outward currents (average amplitude 60 +/- 7 pA) that peaked 2.5 s after the initiation of the inward NMDA currents and decayed with a time constant of 1.4 s. In 43% of those cells exhibiting an outward current, SK channel inhibitors, UCL 1848 (100 nM) and apamin (100 nM) abolished the outward current. In the remainder of the cells, the outward currents were either insensitive or only partly inhibited (44 +/- 4%) by 100 nM UCL 1848. In these cells, the outward currents were reduced by the slow afterhyperpolarization (sAHP) inhibitors, muscarine (3 microM; 43 +/- 9%), UCL 1880 (3 microM; 34 +/- 10%), and UCL 2027 (3 microM; 57 +/- 6%). Neither the BK channel inhibitor, charybdotoxin (100 nM), nor the Na+/K+ ATPase inhibitor, ouabain (100 microM), reduced these outward currents. Irrespective of the pharmacology, the time course of the outward current did not differ. Interestingly, no correlation was observed between the presence of a slow apamin-insensitive afterhyperpolarization and an outward current insensitive to SK channel blockers following NMDA-receptor activation. It is concluded that an NMDA-mediated rise in [Ca2+]i can result in the activation of apamin-sensitive SK channels and of the channels that underlie the sAHP. The activation of these channels may, however, depend on their location relative to NMDA receptors as well as on the spatial Ca2+ buffering within individual neurons.
在电压钳制的海马锥体神经元中，通过N-甲基-D-天冬氨酸（NMDA）受体通道的Ca2+内流可诱导由Ca2+激活的K+通道介导的持久外向电流。我们使用特异性抑制剂试图鉴定这些外向电流背后的通道。在-50 mV的钳制电位下，将1 mM NMDA施加于培养的海马锥体神经元的胞体可诱导预期的内向电流。在44%的测试细胞中，随后出现外向电流（平均幅度60±7 pA），该外向电流在内向NMDA电流开始后2.5 s达到峰值，并以1.4 s的时间常数衰减。在43%表现出外向电流的细胞中，SK通道抑制剂UCL 1848（100 nM）和蜂毒明肽（100 nM）可消除外向电流。在其余细胞中，外向电流对100 nM UCL 1848不敏感或仅部分受抑制（44±4%）。在这些细胞中，外向电流可被慢后超极化（sAHP）抑制剂毒蕈碱（3 μM；43±9%）、UCL 1880（3 μM；34±10%）和UCL 2027（3 μM；57±6%）所降低。BK通道抑制剂蝎毒素（100 nM）和Na+/K+ ATP酶抑制剂哇巴因（100 μM）均不能降低这些外向电流。无论药理学情况如何，外向电流的时间进程并无差异。有趣的是，在NMDA受体激活后，未观察到缓慢的蜂毒明肽不敏感后超极化的存在与对SK通道阻滞剂不敏感的外向电流之间存在相关性。得出的结论是，NMDA介导的细胞内Ca2+浓度升高可导致蜂毒明肽敏感的SK通道以及sAHP背后的通道激活。然而，这些通道的激活可能取决于它们相对于NMDA受体的位置以及单个神经元内的空间Ca2+缓冲作用。
