Anion channels in the retinal pigment epithelium (RPE) play an essential role in the transport of Cl^- between the outer retina and the choroidal blood to regulate the ionic composition and volume of the subretinal fluid that surrounds the photoreceptor outer segments. Recently, we reported that the anion conductance of the mouse RPE basolateral membrane is highly selective for the biologically-active anion thiocyanate (SCN^-), a property that does not correspond with any of the Cl^- channels that have been found to be expressed in the RPE to date. The purpose of this study was to determine the extent to which SLC26A7, a SCN^- permeable-anion exchanger/channel that was reported to be expressed in human RPE, contributes to the RPE basolateral anion conductance. We show by qPCR that Slc26a7 is highly expressed in mouse RPE compared to other members of the Slc26 gene family and Cl^- channel genes known to be expressed in the RPE. By applying immunofluorescence microscopy to mouse retinal sections and isolated cells, we localized SLC26A7 to the RPE basolateral membrane. Finally, we performed whole-cell and excised patch recordings from RPE cells acutely isolated from Slc26a7 knock out mice to show that the SCN^- conductance and permeability of its basolateral membrane are dramatically smaller relative to wild type mouse RPE cells. These findings establish SLC26A7 as the SCN^--selective conductance of the RPE basolateral membrane and provide new insight into the physiology of an anion channel that may participate in anion transport and pH regulation by the RPE.

中文翻译：

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SLC26A7 构成了视网膜色素上皮基底外侧膜的硫氰酸盐选择性阴离子电导。

视网膜色素上皮 (RPE) 中的阴离子通道在 Cl ^-外层视网膜和脉络膜血之间的转运中起重要作用，以调节围绕光感受器外段的视网膜下液的离子组成和体积。最近，我们报道了小鼠RPE基底外侧膜的阴离子传导性的生物活性阴离子硫氰酸（SCN高度选择性^- ），即不与任何的Cl对应的属性^-已发现在待表达的通道迄今为止的 RPE。本研究的目的是确定 SLC26A7（一种 SCN ^-据报道在人 RPE 中表达的渗透性阴离子交换剂/通道有助于 RPE 基底外侧阴离子电导。我们通过 qPCR 表明，与 Slc26 基因家族的其他成员和已知在 RPE 中表达的Cl ^-通道基因相比，Slc26a7 在小鼠 RPE 中高度表达。通过对小鼠视网膜切片和分离细胞应用免疫荧光显微镜，我们将 SLC26A7 定位到 RPE 基底外侧膜。最后，我们对从 Slc26a7 敲除小鼠中急性分离的 RPE 细胞进行了全细胞和切除贴片记录，以表明其基底外侧膜的 SCN ^-电导和通透性相对于野生型小鼠 RPE 细胞显着更小。这些发现将 SLC26A7 确定为 SCN ^--RPE 基底外侧膜的选择性电导，并提供对阴离子通道生理学的新见解，该通道可能参与 RPE 的阴离子转运和 pH 调节。