Initial segment Kv2.2 channels mediate a slow delayed rectifier and maintain high frequency action potential firing in medial nucleus of the trapezoid body neurons
Initial segment Kv2.2 channels mediate a slow delayed rectifier and maintain high frequency action potential firing in medial nucleus of the trapezoid body neurons
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DOI：
10.1113/jphysiol.2008.153734
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发表时间：
2008-07-15
影响因子：
5.5
通讯作者：
Forsythe, Ian D.
中科院分区：
文献类型：
--
作者：
Johnston, Jamie;Griffin, Sarah J.;Forsythe, Ian D.
斜方体内侧核(MNTB)专用于高频放电，在每个盏状巨细胞EPSC中表达Kv3通道和Kv1通道，Kv3通道可缩短动作电位时程，Kv1通道可抑制多个AP放电。然而，MNTB神经元的外向K+电流由另一种未知的延迟整流所主导。它具有缓慢的动力学特性，峰值电导接近37 ns，在-9.2+/-2.1 mV和-35.9+/-1.5 mV时分别处于半激活和半失活状态。非特异性钾通道拮抗剂包括奎宁(100 MM)和高浓度四乙基铵(TEA；IC50=11.8 mM)均可阻断该通道，但未发现特异性拮抗剂。这些特征类似于重组Kv2介导的电流。定量RT-PCR结果显示，Kv2.2基因在MNTB中的表达明显高于Kv2.1基因。Kv2.2抗体显示出特异性染色，Western blotts证实它识别出一种类似于110 kDa的蛋白质，这种蛋白质在Kv2.2基因敲除小鼠的脑干组织中不存在。共聚焦成像显示Kv2.2在MNTB神经元轴突起始段高表达。在缺乏特定拮抗剂的情况下，Hodgkin-Huxley对电压门控电导的模拟表明，Kv2.2在单个AP中的作用很小(由于其缓慢的激活)，但通过在AP重复放电过程中超极化间棘波电位，帮助电压门控钠通道(NAV)从失活中恢复过来。高频激发时的电流钳记录和NAV失活的特征证实了这一假说。我们认为，含Kv2.2的通道在高频放电过程中具有独特的起始段位置，在维持AP幅度方面具有重要作用。
The medial nucleus of the trapezoid body (MNTB) is specialized for high frequency firing by expression of Kv3 channels, which minimize action potential (AP) duration, and Kv1 channels, which suppress multiple AP firing, during each calyceal giant EPSC. However, the outward K+ current in MNTB neurons is dominated by another unidentified delayed rectifier. It has slow kinetics and a peak conductance of similar to 37 nS; it is half-activated at -9.2 +/- 2.1 mV and half-inactivated at -35.9 +/- 1.5 mV. It is blocked by several non-specific potassium channel antagonists including quinine (100 mu M) and high concentrations of extracellular tetraethylammonium (TEA; IC50 = 11.8 mM), but no specific antagonists were found. These characteristics are similar to recombinant Kv2-mediated currents. Quantitative RT-PCR showed that Kv2.2 mRNA was much more prevalent than Kv2.1 in the MNTB. A Kv2.2 antibody showed specific staining and Western blots confirmed that it recognized a protein similar to 110 kDa which was absent in brainstem tissue from a Kv2.2 knockout mouse. Confocal imaging showed that Kv2.2 was highly expressed in axon initial segments of MNTB neurons. In the absence of a specific antagonist, Hodgkin-Huxley modelling of voltage-gated conductances showed that Kv2.2 has a minor role during single APs (due to its slow activation) but assists recovery of voltage-gated sodium channels (Nav) from inactivation by hyperpolarizing interspike potentials during repetitive AP firing. Current-clamp recordings during high frequency firing and characterization of Nav inactivation confirmed this hypothesis. We conclude that Kv2.2-containing channels have a distinctive initial segment location and crucial function in maintaining AP amplitude by regulating the interspike potential during high frequency firing.