Caldwell J H, Schaller K L, Lasher R S, Peles E, Levinson S R
Department of Cellular and Structural Biology, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, Denver, CO 80262, USA.
Proc Natl Acad Sci U S A. 2000 May 9;97(10):5616-20. doi: 10.1073/pnas.090034797.
Voltage-gated sodium channels perform critical roles for electrical signaling in the nervous system by generating action potentials in axons and in dendrites. At least 10 genes encode sodium channels in mammals, but specific physiological roles that distinguish each of these isoforms are not known. One possibility is that each isoform is expressed in a restricted set of cell types or is targeted to a specific domain of a neuron or muscle cell. Using affinity-purified isoform-specific antibodies, we find that Na(v)1.6 is highly concentrated at nodes of Ranvier of both sensory and motor axons in the peripheral nervous system and at nodes in the central nervous system. The specificity of this antibody was also demonstrated with the Na(v)1.6-deficient mouse mutant strain med, whose nodes were negative for Na(v)1.6 immunostaining. Both the intensity of labeling and the failure of other isoform-specific antibodies to label nodes suggest that Na(v)1.6 is the predominant channel type in this structure. In the central nervous system, Na(v)1.6 is localized in unmyelinated axons in the retina and cerebellum and is strongly expressed in dendrites of cortical pyramidal cells and cerebellar Purkinje cells. Ultrastructural studies indicate that labeling in dendrites is both intracellular and on dendritic shaft membranes. Remarkably, Na(v)1.6 labeling was observed at both presynaptic and postsynaptic membranes in the cortex and cerebellum. Thus, a single sodium channel isoform is targeted to different neuronal domains and can influence both axonal conduction and synaptic responses.
电压门控钠通道通过在轴突和树突中产生动作电位，在神经系统的电信号传导中发挥关键作用。在哺乳动物中，至少有10个基因编码钠通道，但这些异构体各自独特的生理作用尚不清楚。一种可能性是，每种异构体在一组特定的细胞类型中表达，或者定位于神经元或肌肉细胞的特定区域。使用亲和纯化的异构体特异性抗体，我们发现Na(v)1.6在外周神经系统的感觉和运动轴突的郎飞结以及中枢神经系统的节点处高度集中。Na(v)1.6缺陷小鼠突变株med的节点对Na(v)1.6免疫染色呈阴性，这也证明了该抗体的特异性。标记强度以及其他异构体特异性抗体未能标记节点都表明，Na(v)1.6是该结构中主要的通道类型。在中枢神经系统中，Na(v)1.6定位于视网膜和小脑中的无髓鞘轴突，并在皮质锥体细胞和小脑浦肯野细胞的树突中强烈表达。超微结构研究表明，树突中的标记既存在于细胞内，也存在于树突轴膜上。值得注意的是，在皮质和小脑中的突触前膜和突触后膜上均观察到Na(v)1.6标记。因此，单一的钠通道异构体定位于不同的神经元区域，并可影响轴突传导和突触反应。
