Guan D, Lee J C F, Tkatch T, Surmeier D J, Armstrong W E, Foehring R C
Department of Anatomy and Neurobiology, University of Tennessee, 855 Monroe Avenue, Memphis, TN 38163, USA.
J Physiol. 2006 Mar 1;571(Pt 2):371-89. doi: 10.1113/jphysiol.2005.097006. Epub 2005 Dec 22.
Potassium channels are extremely diverse regulators of neuronal excitability. As part of an investigation into how this molecular diversity is utilized by neurones, we examined the expression and biophysical properties of native Kv1 channels in layer II/III pyramidal neurones from somatosensory and motor cortex. Single-cell RT-PCR, immunocytochemistry, and whole cell recordings with specific peptide toxins revealed that individual pyramidal cells express multiple Kv1 alpha-subunits. The most abundant subunit mRNAs were Kv1.1 > 1.2 > 1.4 > 1.3. All of these subunits were localized to somatodendritic as well as axonal cell compartments. These data suggest variability in the subunit complexion of Kv1 channels in these cells. The alpha-dendrotoxin (alpha-DTX)-sensitive current activated more rapidly and at more negative potentials than the alpha-DTX-insensitive current, was first observed at voltages near action potential threshold, and was relatively insensitive to holding potential. The alpha-DTX-sensitive current comprised about 10% of outward current at steady-state, in response to steps from -70 mV. From -50 mV, this percentage increased to approximately 20%. All cells expressed an alpha-DTX-sensitive current with slow inactivation kinetics. In some cells a transient component was also present. Deactivation kinetics were voltage dependent, such that deactivation was slow at potentials traversed by interspike intervals during repetitive firing. Because of its kinetics and voltage dependence, the alpha-DTX-sensitive current should be most important at physiological resting potentials and in response to brief stimuli. Kv1 channels should also be important at voltages near threshold and corresponding to interspike intervals.
钾通道是神经元兴奋性极为多样的调节因子。作为对神经元如何利用这种分子多样性的研究的一部分，我们检测了体感和运动皮层II/III层锥体神经元中天然Kv1通道的表达和生物物理特性。单细胞逆转录聚合酶链反应、免疫细胞化学以及使用特异性肽毒素的全细胞记录显示，单个锥体细胞表达多种Kv1α亚基。最丰富的亚基mRNA为Kv1.1 > 1.2 > 1.4 > 1.3。所有这些亚基均定位于胞体树突以及轴突细胞区室。这些数据表明这些细胞中Kv1通道的亚基组成存在变异性。α-树眼镜蛇毒素（α-DTX）敏感电流比α-DTX不敏感电流激活更快且在更负的电位下激活，首次在接近动作电位阈值的电压下观察到，并且对钳制电位相对不敏感。在稳态下，响应于从-70 mV的阶跃，α-DTX敏感电流约占外向电流的10%。从-50 mV起，该百分比增加到约20%。所有细胞均表达具有缓慢失活动力学的α-DTX敏感电流。在一些细胞中还存在一个瞬态成分。失活动力学是电压依赖性的，使得在重复放电期间峰间间隔所跨越的电位下失活缓慢。由于其动力学和电压依赖性，α-DTX敏感电流在生理静息电位以及对短暂刺激的响应中应该最为重要。Kv1通道在接近阈值以及对应于峰间间隔的电压下也应该很重要。
