CALCIUM HOMEOSTASIS IN MAMMALIAN ROD AND CONE PHOTORECEPTORS

摘要 钙离子（Ca2+）是一种普遍存在的信号分子，控制着细胞的功能和存活 的神经元。在广泛的感光细胞突变中被破坏的Ca2+稳态 被认为会导致细胞死亡视网膜退化和失明在脊椎动物 光感受器，Ca2+的变化也调节光转导的关闭 级联加速光响应恢复和背景适应。据认为 脊椎动物光感受器外节中的Ca 2+浓度 通过cGMP门控（CNG）通道流入之间的动态平衡控制 和通过细胞特异性Na +/Ca2+，K+交换剂（NCKX）的挤出，杆中的NCKX 1和 NCKX2在锥体中。然而，这些交换剂控制Ca2+的程度 哺乳动物光感受器和调节光转导和细胞内稳态 存活率尚未确定。此外，尚不清楚是否有其他活跃或 在哺乳动物的外节中， 视杆细胞和视锥细胞。我们将进行实验以确定CNG和NCKX1在 调节哺乳动物视杆细胞中的Ca 2+稳态及其对长期视杆细胞的影响 生存和退化。我们还将检验异常感光细胞 Ca2+稳态介导多种致盲性疾病中的光感受器变性 并将确定恢复Ca2+流量平衡的治疗潜力， 光感受器通道病我们已经确定NCKX 4是第二个Na +/Ca2+，K + 在哺乳动物视锥细胞中表达的交换器。我们将进行实验来分析 NCKX2-和NCKX4-的表达谱、形态和功能特性 缺乏小鼠视锥细胞这些实验将建立分子机制， 从哺乳动物视锥细胞中有效挤出Ca2+对于快速 视锥细胞作为我们白天光感受器的反应动力学和背景适应 以及它们对视锥细胞长期存活和退化的影响。总体而言，我们 实验将建立介导Ca2+挤出的分子机制 哺乳动物的感光细胞。它们还将帮助我们理解 异常的Ca2+稳态和感光细胞变性，并可能导致 对发展通道变性的治疗。

ABSTRACT Calcium (Ca2+) is a ubiquitous signaling molecule that controls the function and survival of neurons. The disrupted Ca2+ homeostasis in a wide range of photoreceptor mutations is believed to cause cell death, retinal degeneration and blindness. In vertebrate photoreceptors, Ca2+ changes also modulate the shutoff of the phototransduction cascade to accelerate light response recovery and background adaptation. It is thought that the concentration of Ca2+ in the outer segments of vertebrate photoreceptors is controlled by a dynamic balance between influx via the cGMP-gated (CNG) channels and extrusion via cell-specific Na+/Ca2+, K+ exchangers (NCKX), NCKX1 in rods and NCKX2 in cones. However, the extent to which these exchangers control the Ca2+ homeostasis in mammalian photoreceptors and modulate phototransduction and cell survival has not been determined. In addition, it is not known whether other active or passive mechanisms for extruding Ca2+ are at play in the outer segments of mammalian rods and cones. We will perform experiments to establish the role of CNG and NCKX1 in regulating the Ca2+ homeostasis in mammalian rods and their effect on long-term rod survival and degeneration. We will also test the hypothesis that abnormal photoreceptor Ca2+ homeostasis mediates photoreceptor degeneration in a variety of blinding diseases and will determine the therapeutic potential of restoring the Ca2+ flux balance in photoreceptor channelopathies. We have identified NCKX4 as a second Na+/Ca2+, K+ exchanger expressed in mammalian cones. We will perform experiments to analyze the expression profile, morphology, and functional properties of NCKX2- and NCKX4- deficient mouse cones. These experiments will establish the molecular mechanisms for the efficient extrusion of Ca2+ from mammalian cone photoreceptors critical for the fast response kinetics and background adaptation of cones as our daytime photoreceptors as well as their effect on cone long-term survival and degeneration. Collectively, our experiments will establish the molecular mechanisms that mediate the extrusion of Ca2+ from mammalian photoreceptors. They will also help us understand the link between abnormal Ca2+ homeostasis and photoreceptor degeneration and might potentially lead to the development of treatments for channelopaties.