Human Nav1.6 Channels Generate Larger Resurgent Currents than Human Nav1.1 Channels, but the Navβ4 Peptide Does Not Protect Either Isoform from Use-Dependent Reduction.
Human Nav1.6 Channels Generate Larger Resurgent Currents than Human Nav1.1 Channels, but the Navβ4 Peptide Does Not Protect Either Isoform from Use-Dependent Reduction.
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DOI：
10.1371/journal.pone.0133485
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发表时间：
2015
期刊：
影响因子：
3.7
通讯作者：
Cummins TR
中科院分区：
文献类型：
--
作者：
Patel RR;Barbosa C;Xiao Y;Cummins TR
电压门控钠通道负责动作电位（AP）的启动和传播。两种脑亚型Nav1.1和Nav1.6具有非常不同的细胞和亚细胞表达。具体地说，Nav1.1主要表达在快速发放GABA能神经元的索马和近端轴突起始段，而Nav1.6则在快速发放GABA能神经元和兴奋性神经元的远端轴突起始段和郎维尔结中发现。有趣的是，一个辅助电压门控钠通道亚基Navβ4也在快速发放GABA能神经元的轴突起始段富集。认为Navβ4的C末端尾部介导复活钠电流，这是一种在动作电位后立即发生的非典型电流，预计可增强兴奋性。为了更好地理解Nav1.1、Nav1.6和Navβ4对高频放电的贡献，我们比较了在存在和不存在对应于Navβ4的部分C末端尾的肽的情况下这两种通道亚型的性质。我们使用全细胞膜片钳记录来检查HEK293T细胞中这两种通道亚型的生物物理特性，并发现人Nav1.1和Nav1.6电流之间存在一些差异。Nav1.1通道比Nav1.6通道表现出更慢的闭合状态失活，但更快的开放状态失活。我们还观察到Nav1.6产生复苏电流的倾向更大，最可能是由于其与Nav1.1相比，开放状态失活的动力学较慢。这两种亚型对慢AP波形和快AP波形也显示出不同的反应，这些反应被Navβ4肽改变。尽管Navβ4肽显著增加了表观失活的恢复率，但Navβ4肽不能保护任一通道亚型免受10 Hz步进脉冲刺激或慢或快AP波形序列的使用依赖性降低。总的来说，这两个通道具有不同的生物物理特性，可能差异有助于调节神经元的兴奋性。
Voltage-gated sodium channels are responsible for the initiation and propagation of action potentials (APs). Two brain isoforms, Nav1.1 and Nav1.6, have very distinct cellular and subcellular expression. Specifically, Nav1.1 is predominantly expressed in the soma and proximal axon initial segment of fast-spiking GABAergic neurons, while Nav1.6 is found at the distal axon initial segment and nodes of Ranvier of both fast-spiking GABAergic and excitatory neurons. Interestingly, an auxiliary voltage-gated sodium channel subunit, Navβ4, is also enriched in the axon initial segment of fast-spiking GABAergic neurons. The C-terminal tail of Navβ4 is thought to mediate resurgent sodium current, an atypical current that occurs immediately following the action potential and is predicted to enhance excitability. To better understand the contribution of Nav1.1, Nav1.6 and Navβ4 to high frequency firing, we compared the properties of these two channel isoforms in the presence and absence of a peptide corresponding to part of the C-terminal tail of Navβ4. We used whole-cell patch clamp recordings to examine the biophysical properties of these two channel isoforms in HEK293T cells and found several differences between human Nav1.1 and Nav1.6 currents. Nav1.1 channels exhibited slower closed-state inactivation but faster open-state inactivation than Nav1.6 channels. We also observed a greater propensity of Nav1.6 to generate resurgent currents, most likely due to its slower kinetics of open-state inactivation, compared to Nav1.1. These two isoforms also showed differential responses to slow and fast AP waveforms, which were altered by the Navβ4 peptide. Although the Navβ4 peptide substantially increased the rate of recovery from apparent inactivation, Navβ4 peptide did not protect either channel isoform from undergoing use-dependent reduction with 10 Hz step-pulse stimulation or trains of slow or fast AP waveforms. Overall, these two channels have distinct biophysical properties that may differentially contribute to regulating neuronal excitability.