Du J, Tao-Cheng J H, Zerfas P, McBain C J
Laboratory of Cellular and Molecular Neurophysiology, NICHD-NIH, USA.
Neuroscience. 1998 May;84(1):37-48. doi: 10.1016/s0306-4522(97)00519-8.
A variety of voltage-gated ion channels are expressed on principal cell dendrites and have been proposed to play a pivotal role in the regulation of dendritic excitability. Previous studies at the light microscopic level demonstrated that the K+ channel subunit Kv2.1 expression was polarized to the cell soma and dendrites of principal neurons throughout the central nervous system. Here, using double immunostaining we now show that Kv2.1 protein is similarly expressed in the majority of cortical and hippocampal parvalbumin, calbindin and somatostatin-containing inhibitory interneurons. At the electron microscopic level Kv2.1 immunoreactivity was primarily observed on the plasma membrane of the somata and proximal dendrites of both principal neurons and inhibitory interneurons; expression was low on smaller dendritic branches, and absent on axons and presynaptic terminals. Kv2.1 subunit expression was highly concentrated on the cell surface membrane immediately facing astrocytic processes. Kv2.1 expression was also concentrated in specific cytoplasmic compartments and on the subsurface cisterns underlying the plasma membrane facing astrocytes. In addition, Kv2.1 subunit immunoreactivity was associated with postsynaptic densities of a fraction of inhibitory symmetric synapses; while expression at asymmetric synapses was rare. These data demonstrate that channels formed by Kv2.1 subunits are uniquely positioned on the soma and principal dendrites of both pyramidal cells and inhibitory interneurons at sites immediately adjacent to astrocytic processes. This close apposition to astrocytes will ensure a rapid removal and limit the influence of K+ released into the extracellular space. This expression pattern suggests that channels formed by Kv2.1 are poised to provide a role in the regulation of neuronal dendritic excitability.
多种电压门控离子通道在主细胞树突上表达，并被认为在树突兴奋性调节中起关键作用。先前在光学显微镜水平的研究表明，钾离子通道亚基Kv2.1的表达在整个中枢神经系统的主神经元的细胞体和树突上呈极化分布。在这里，我们使用双重免疫染色表明，Kv2.1蛋白在大多数皮质和海马小白蛋白、钙结合蛋白和含生长抑素的抑制性中间神经元中也有类似表达。在电子显微镜水平上，主要在主神经元和抑制性中间神经元的细胞体和近端树突的质膜上观察到Kv2.1免疫反应性；在较小的树突分支上表达较低，在轴突和突触前终末上则没有表达。Kv2.1亚基表达高度集中在紧邻星形胶质细胞突起的细胞表面膜上。Kv2.1表达也集中在特定的细胞质区室以及面向星形胶质细胞的质膜下方的亚表面池上。此外，Kv2.1亚基免疫反应性与一部分抑制性对称突触的突触后致密物相关；而在不对称突触处的表达很少见。这些数据表明，由Kv2.1亚基形成的通道独特地定位在锥体细胞和抑制性中间神经元的细胞体和主要树突上，位于紧邻星形胶质细胞突起的部位。与星形胶质细胞的这种紧密毗邻将确保快速清除并限制释放到细胞外空间中的钾离子的影响。这种表达模式表明，由Kv2.1形成的通道准备好在调节神经元树突兴奋性中发挥作用。
