ION CONDUCTANCES IN THE RETINAL PIGMENT EPITHELIUM

光感受器的健康和完整性关键取决于其细胞外微环境的组成和体积。通过离子、水和代谢物穿过视网膜色素上皮（RPE）（在感光器外节和脉络膜血液供应之间并列的单层细胞）的运输来实现对该所谓的视网膜下空间的离子组成和体积的调节。RPE转运是位于顶膜和基底外侧膜中的离子泵、共转运蛋白、交换剂和通道的不同组的协调活性的结果。随着视网膜活动的变化，视网膜细胞释放的化学信号也扩散到RPE，其中运输被调节以补偿感光器微环境的改变。这些运输过程或其调节的中断可能导致视网膜下腔的不利变化，从而导致视网膜疾病。这些转运途径还负责维持RPE细胞中的细胞内组成，如果受到干扰，可能会对其他关键RPE功能（如维生素A转运和代谢）产生不利影响。我们的总体目标是了解钾（K+）通道参与调节视网膜下腔和RPE细胞质中液体的体积和离子组成的机制。具体目标是：（1）确定RPE内向整流K+（Kir）电导的分子基础，（2）确定Kir通道受细胞内ATP调节的机制，（3）了解Kir通道是如何受细胞内pH的生理变化调节的，（4）了解Kir通道在细胞内pH的变化对Kir通道的影响。和（4）验证另一种K+通道（M型K+通道）的容积诱导激活由花生四烯酸代谢物介导的假设。这些目标将采用分子和电生理技术相结合的方法来研究K+通道的结构、功能和调节。这些研究的结果将更好地了解这些至关重要的转运蛋白如何在RPE中运作，以维持健康的感光细胞微环境。

The health and integrity of photoreceptors critically depend on the composition and volume of their extracellular microenvironment. Regulation of the ionic composition and volume of this so-called subretinal space is accomplished by the transport of ions, water, and metabolites across the retinal pigment epithelium (RPE), a monolayer of cells juxtaposed between the photoreceptor outer segments and the choroidal blood supply. RPE transport is the result of the coordinated activity of a diverse group of ion pumps, co-transporters , exchangers, and channels residing in the apical and basolateral membranes. With changes in retinal activity, chemical signals released by retinal cell diffuse too the RPE where transport is adjusted to compensate for alteration in the photoreceptor microenvironment. Disruption of these transport processes or their regulation may cause adverse changes in the subretinal space, contributing to retinal disease. These transport pathways are also responsible for maintaining the intracellular composition in the RPE cell, which, if disturbed, could adversely affect other key RPE functions such as vitamin A transport and metabolism. Our overall goal is to understand the mechanisms by which potassium (K+) channels participate in the regulation of the volume and ionic composition of the fluid in both the subretinal space and the RPE cytoplasm. The specific aims are: (1) To determine the molecular basis for the inwardly rectifying K+ (Kir) conductance of the RPE; (2) To determine the mechanism underlying the regulation of the Kir channel by intracellular ATP; (3) To understand how the Kir channel is modulated by physiological changes in intracellular pH; and (4) To test the hypothesis that volume-induced activation of another K+ channel, an M-type K+ channel, is mediated by arachidonic acid metabolites. These aims will be pursued using a combination of molecular and electrophysiological techniques to investigate K+ channel structure, function, and regulation. The outcome of these studies will be a better understanding of how these critically important transport proteins operate in the RPE to maintain a healthy photoreceptor microenvironment.