Paul Flechsig Institute of Brain Research, University of Leipzig, Leipzig, Germany.
PLoS One. 2011 Jan 21;6(1):e16106. doi: 10.1371/journal.pone.0016106.
Glial cells such as retinal Müller glial cells are involved in potassium ion and water homeostasis of the neural tissue. In these cells, inwardly rectifying potassium (Kir) channels and aquaporin-4 water channels play an important role in the process of spatial potassium buffering and water drainage. Moreover, Kir4.1 channels are involved in the maintenance of the negative Müller cell membrane potential. The subcellular distribution of Kir4.1 and aquaporin-4 channels appears to be maintained by interactions with extracellular and intracellular molecules. Laminins in the extracellular matrix, dystroglycan in the membrane, and dystrophins in the cytomatrix form a complex mediating the polarized expression of Kir4.1 and aquaporin-4 in Müller cells.
METHODOLOGY/PRINCIPAL FINDINGS: The aim of the present study was to test the function of the β2 and γ3 containing laminins in murine Müller cells. We used knockout mice with genetic deletion of both β2 and γ3 laminin genes to assay the effects on Kir4.1 and aquaporin-4. We studied protein and mRNA expression by immunohistochemistry, Western Blot, and quantitative RT-PCR, respectively, and membrane currents of isolated cells by patch-clamp experiments. We found a down-regulation of mRNA and protein of Kir4.1 as well as of aquaporin-4 protein in laminin knockout mice. Moreover, Müller cells from laminin β2 and γ3 knockout mice had reduced Kir-mediated inward currents and their membrane potentials were more positive than those in age-matched wild-type mice.
These findings demonstrate a strong impact of laminin β2 and γ3 subunits on the expression and function of both aquaporin-4 and Kir4.1, two important membrane proteins in Müller cells.
神经组织中的胶质细胞（如视网膜 Müller 胶质细胞）参与钾离子和水的动态平衡。在这些细胞中，内向整流钾（Kir）通道和水通道蛋白-4（AQP4）通道在空间钾缓冲和水排出过程中发挥重要作用。此外，Kir4.1 通道参与维持负性 Müller 细胞膜电位。Kir4.1 和 AQP4 通道的亚细胞分布似乎通过与细胞外和细胞内分子的相互作用得以维持。细胞外基质中的层粘连蛋白、膜中的 dystroglycan 和细胞基质中的 dystrophin 形成复合物，介导 Müller 细胞中 Kir4.1 和 AQP4 的极化表达。
方法/主要发现：本研究旨在测试含有β2 和 γ3 亚基的层粘连蛋白在小鼠 Müller 细胞中的功能。我们使用同时缺失β2 和 γ3 层粘连蛋白基因的基因敲除小鼠来检测对 Kir4.1 和 AQP4 的影响。我们分别通过免疫组织化学、Western blot 和定量 RT-PCR 研究蛋白和 mRNA 表达，并通过膜片钳实验研究分离细胞的膜电流。我们发现，在层粘连蛋白敲除小鼠中，Kir4.1 和 AQP4 的 mRNA 和蛋白表达均下调，AQP4 蛋白表达下调。此外，层粘连蛋白β2 和 γ3 敲除小鼠的 Müller 细胞中 Kir 介导的内向电流减少，其膜电位比同龄野生型小鼠更正。
这些发现表明层粘连蛋白β2 和 γ3 亚基对 Müller 细胞中两种重要膜蛋白 AQP4 和 Kir4.1 的表达和功能具有强烈影响。
