Brasko C, Hawkins V, De La Rocha I Chacon, Butt A M
Institute of Biology and Biomedical Sciences, School of Pharmacy and Biomedical Sciences, University of Portsmouth, St Michael's Building, White Swan Road, Portsmouth, PO1 2DT, UK.
Brain Struct Funct. 2017 Jan;222(1):41-59. doi: 10.1007/s00429-016-1199-8. Epub 2016 Feb 15.
The inwardly rectifying K channel subtype Kir5.1 is only functional as a heteromeric channel with Kir4.1. In the CNS, Kir4.1 is localised to astrocytes and is the molecular basis of their strongly negative membrane potential. Oligodendrocytes are the specialised myelinating glia of the CNS and their resting membrane potential provides the driving force for ion and water transport that is essential for myelination. However, little is known about the ion channel profile of mature myelinating oligodendrocytes. Here, we identify for the first time colocalization of Kir5.1 with Kir4.1 in oligodendrocytes in white matter. Immunolocalization with membrane-bound Na/K-ATPase and western blot of the plasma membrane fraction of the optic nerve, a typical CNS white matter tract containing axons and the oligodendrocytes that myelinate them, demonstrates that Kir4.1 and Kir5.1 are colocalized on oligodendrocyte cell membranes. Co-immunoprecipitation provides evidence that oligodendrocytes and astrocytes express a combination of homomeric Kir4.1 and heteromeric Kir4.1/Kir5.1 channels. Genetic knock-out and shRNA to ablate Kir4.1 indicates plasmalemmal expression of Kir5.1 in glia is largely dependent on Kir4.1 and the plasmalemmal anchoring protein PSD-95. The results demonstrate that, in addition to astrocytes, oligodendrocytes express both homomeric Kir4.1 and heteromeric Kir4.1/Kir5.1 channels. In astrocytes, these channels are essential to their key functions of K uptake and CO/H chemosensation. We propose Kir4.1/Kir5.1 channels have equivalent functions in oligodendrocytes, maintaining myelin integrity in the face of large ionic shifts associated with action potential propagation along myelinated axons.
内向整流钾通道亚型Kir5.1仅作为与Kir4.1形成的异源通道发挥功能。在中枢神经系统中，Kir4.1定位于星形胶质细胞，是其强负膜电位的分子基础。少突胶质细胞是中枢神经系统中专门负责髓鞘形成的神经胶质细胞，其静息膜电位为髓鞘形成所必需的离子和水运输提供驱动力。然而，对于成熟的髓鞘形成少突胶质细胞的离子通道谱了解甚少。在此，我们首次发现白质少突胶质细胞中Kir5.1与Kir4.1共定位。通过与膜结合的钠钾ATP酶进行免疫定位以及对视神经质膜部分进行蛋白质印迹分析（视神经是包含轴突及其髓鞘形成少突胶质细胞的典型中枢神经系统白质束），结果表明Kir4.1和Kir5.1共定位于少突胶质细胞膜上。免疫共沉淀提供了证据，表明少突胶质细胞和星形胶质细胞表达同型Kir4.1和异型Kir4.1/Kir5.1通道的组合。通过基因敲除和短发夹RNA消除Kir4.1表明，胶质细胞中Kir5.1的质膜表达在很大程度上依赖于Kir4.1和质膜锚定蛋白PSD - 95。结果表明，除了星形胶质细胞外，少突胶质细胞也表达同型Kir4.1和异型Kir4.1/Kir5.1通道。在星形胶质细胞中，这些通道对于其钾摄取和二氧化碳/氢离子化学感受的关键功能至关重要。我们推测Kir4.1/Kir5.1通道在少突胶质细胞中具有同等功能，在面对与动作电位沿有髓轴突传播相关的大量离子变化时维持髓鞘完整性。
