KCNQ channels mediate IKs, a slow K+ current regulating excitability in the rat node of Ranvier
KCNQ channels mediate IKs, a slow K+ current regulating excitability in the rat node of Ranvier
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DOI：
10.1113/jphysiol.2006.106815
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发表时间：
2006-05-15
影响因子：
5.5
通讯作者：
Bostock, H.
中科院分区：
文献类型：
--
作者：
Schwarz, J. R.;Glassmeier, G.;Bostock, H.
降低KCNQ2通道功能的突变会导致神经元过度兴奋，表现为癫痫发作和肌肉痉挛。这些通道存在于大鼠脑和神经的Ranvier结节，被认为是介导慢节钾电流I(Ks)的通道。我们使用免疫细胞化学、电生理学和药理学来验证这一假说，并确定KCNQ通道对大鼠神经兴奋性的贡献。当用KCNQ2和KCNQ3抗体对坐骨神经有髓神经纤维进行免疫荧光显微镜检查时，所有的结节都显示出强的KCNQ2免疫反应。大约一半的中小型纤维的结节都有KCNQ2和KCNQ3的标记，但大纤维的结节只有KCNQ2抗体标记。在大纤维电压钳实验中，选择性KCNQ通道阻断剂XE991(IC(50)=2.2mM)和利诺匹定(IC(50)=5.5mM)和TEA(IC(50)=0.22 mM)完全抑制iKs。KCNQ通道开放剂雷替加宾(10 MM)使激活曲线向更负的膜电位移动-24 mV，从而增加了iKs。在等渗氯化钾中，50%的I(Ks)在-62 mV时被激活。随着[K(+)](O)的降低，激活曲线向正电位移动，从而使iKs的药理和生物物理特性与异源表达的同源KCNQ2通道的药理和生物物理特性一致。进一步利用XE991选择性阻断IKS的能力来研究IKS在体内的作用。在麻醉大鼠中，尾部运动轴突起的兴奋性由诱发40%的最大复合肌肉动作电位所需的刺激电流来表示。XE991(2.5 mg kg(-1)I.P.)消除了以前归因于iKs的所有神经兴奋性功能：适应100 ms的亚阈值去极化电流，后去极化的兴奋性不足，以及在单个脉冲或短脉冲序列后的晚期亚兴奋性。由于XE991治疗后尖峰频率适应性降低，100ms的阈值以上电流注射产生了长串动作电位。结论：大鼠坐骨神经大纤维的IKs电流是由KCNQ通道介导的，KCNQ通道在大鼠坐骨神经的大纤维中可能是KCNQ2同源异构体。
Mutations that reduce the function of KCNQ2 channels cause neuronal hyperexcitability, manifested as epileptic seizures and myokymia. These channels are present in nodes of Ranvier in rat brain and nerve and have been proposed to mediate the slow nodal potassium current I(Ks). We have used immunocytochemistry, electrophysiology and pharmacology to test this hypothesis and to determine the contribution of KCNQ channels to nerve excitability in the rat. When myelinated nerve fibres of the sciatic nerve were examined by immunofluorescence microscopy using antibodies against KCNQ2 and KCNQ3, all nodes showed strong immunoreactivity for KCNQ2. The nodes of about half the small and intermediate sized fibres showed labelling for both KCNQ2 and KCNQ3, but nodes of large fibres were labelled by KCNQ2 antibodies only. In voltage-clamp experiments using large myelinated fibres, the selective KCNQ channel blockers XE991 (IC(50) = 2.2 mu M) and linopirdine (IC(50) = 5.5 mu M) completely inhibited IKs, as did TEA (IC(50) = 0.22mM). The KCNQ channel opener retigabine (10 mu M) shifted the activation curve to more negative membrane potentials by - 24 mV, thereby increasing IKs. In isotonic KCl 50% of I(Ks) was activated at -62 mV. The activation curve shifted to more positive potentials as [K(+)](o) was reduced, so that the pharmacological and biophysical properties of IKs were consistent with those of heterologously expressed homomeric KCNQ2 channels. The ability of XE991 to selectively block IKs was further exploited to study IKs function in vivo. In anaesthetized rats, the excitability of tail motor axons was indicated by the stimulus current required to elicit a 40% of maximal compound muscle action potential. XE991 (2.5 mg kg(-1) I. P.) eliminated all nerve excitability functions previously attributed to IKs: accommodation to 100 ms subthreshold depolarizing currents, the post-depolarization undershoot in excitability, and the late subexcitability after a single impulse or short trains of impulses. Due to reduced spike-frequency adaptation after XE991 treatment, 100 ms suprathreshold current injections generated long trains of action potentials. We conclude that the nodal IKs current is mediated by KCNQ channels, which in large fibres of rat sciatic nerve appear to be KCNQ2 homomers.