CALCIUM HOMEOSTASIS IN MAMMALIAN ROD AND CONE PHOTORECEPTORS

摘要 钙(Ca~(2+))是一种普遍存在的信号分子，控制着细胞的功能和生存 神经细胞的。大范围光感受器突变中钙离子稳态的破坏 被认为会导致细胞死亡、视网膜退化和失明。在脊椎动物中 光感受器、钙离子的变化也调制了光信号转导的关闭 级联以加速光响应恢复和背景适应。它被认为是 脊椎动物光感受器外节的钙离子浓度是 通过cGMP门控(CNG)通道的内流之间的动态平衡控制 以及通过细胞特异的Na+/Ca2+，K+交换器(NCKX)，NCKX1在杆状和 NCKX2在圆锥体中。然而，这些交换器控制钙离子的程度 哺乳动物光感受器的动态平衡及其对光转导和细胞的调控 生死存亡尚未确定。此外，尚不清楚是否有其他活跃的或 被动的钙排出机制在哺乳动物的外节中起作用 杆状和圆锥状。我们将进行实验以确定CNG和NCKX1在 哺乳动物视杆细胞钙稳态的调节及其对长期视杆细胞的影响 生存和退化。我们还将检验这样一种假设，即异常感光细胞 钙离子稳态在多种致盲疾病中介导光感受器退化 并将确定恢复钙离子流量平衡的治疗潜力 光感受器通道病。我们已鉴定NCKX4为第二个Na+/Ca~(2+)，K~+ 在哺乳动物圆锥体中表达的交换器。我们将进行实验来分析 NCKX2-和NCKX4-的表达谱、形态和功能特性 有缺陷的老鼠锥体。这些实验将建立分子机制， 哺乳动物视锥感光细胞中钙离子的有效排出对FAST至关重要 视锥细胞作为白天光感受器的反应动力学和背景适应 以及它们对锥体长期存活和退化的影响。总的来说，我们的 实验将建立起调节钙离子排出的分子机制 来自哺乳动物的光感受器。它们还将帮助我们了解 钙离子稳态异常与光感受器退变可能导致 对治疗沟道病的发展做出了贡献。

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.