NMDA modulates sodium and calcium retinal channels

描述（由申请人提供）：本提案旨在表征视网膜水平细胞中NMDA对电压门控钠电流和钙电流的调节，探索调节发生的机制，并观察远端视网膜中NMDA的功能意义。NMDA受体在脑中的作用已被深入研究，涉及长时程增强，兴奋性毒性和神经发育和可塑性。然而，在远端视网膜中，NMDA受体的作用尚不清楚。基于初步数据，将测试的模型是水平细胞中NMDA受体的激活导致钙通过NMDA通道和CICR从咖啡因敏感的细胞内储存流入。NMDA诱导的电压敏感性钠和钙电导的抑制依赖于此以及钙结合蛋白钙调蛋白的激活。 由光响应编码的信息类型包括与刺激亮度、神经递质增益功效、对比度检测以及视网膜的亮暗条件有关的细节。因此，在开发出足够的人工视网膜用于临床目的之前，以及在治疗影响视网膜的疾病（如帕金森氏症）之前，了解电压门控通道如何有助于编码这种视觉信息是至关重要的。本提案中概述的三个具体目标旨在：I）检验NMDA受体激活抑制鲶鱼视锥水平细胞中发现的电压门控钠电流和电压门控钙电流的假设，II）检验NMDA有助于鲶鱼视锥水平细胞中光响应和暗静息膜电位的形成的假设，和III）以检验钙依赖性信号传导途径将鲶鱼视锥水平细胞中NMDA受体的活化与电压门控钠和钙通道的抑制联系起来的假设。这些具体的目标将使用多学科的方法结合电生理学，药理学和免疫细胞化学和钙成像技术进行。使用分离的细胞和视网膜切片制备获得的结果将显著有助于本研究的长期目标，即了解电压门控通道如何影响通过脊椎动物视网膜传递的视觉信息。

DESCRIPTION (provided by applicant): This proposal is designed to characterize the modulation of voltage-gated sodium and calcium currents by NMDA in retinal horizontal cells, to explore the mechanism by which modulation occurs and to look at functional implications of NMDA in the distal retina. The role of NMDA receptors in brain has been intensely examined in relation to long-term potentiation, excitotoxicity and neural development and plasticity. However, in the distal retina, the role of the NMDA receptor is unclear. Based on preliminary data, the model that will be tested is that activation of the NMDA receptor in horizontal cells results in calcium influx through the NMDA channel and CICR from caffeine-sensitive intracellular stores. NMDA-induced inhibition of the voltage-sensitive sodium and calcium conductance is dependent on this and the activation of the calcium binding protein, calmodulin. The type of information encoded by the light response includes details pertaining to stimulus brightness, neurotransmitter gain efficacy, contrast detection and the light and dark condition of the retina. Therefore, it is essential to understand how voltage-gated channels contribute to the encoding of this visual information before adequate artificial retinas can be developed for clinical purposes and before treatments for diseases that affect the retina, such as Parkinson's, can be effective. The three specific aims outlined in this proposal are designed to: I) to test the hypothesis that NMDA receptor activation inhibits both the voltage-gated sodium and voltage-gated calcium currents found in catfish cone horizontal cells, II) to test the hypothesis that NMDA contributes to formation of the light response and the dark resting membrane potential in catfish cone horizontal cells, and III) to test the hypothesis that calcium dependent signaling pathways link activation of NMDA receptors to inhibition of the voltage-gated sodium and calcium channels in catfish cone horizontal cells. These specific aims will be carried out using a multidisciplinary approach combining electrophysiological, pharmacological and immunocytochemical and calcium imaging techniques. Results obtained using isolated cells and a retinal slice preparation will contribute significantly to the long-range goal of this research, which is to understand how voltage-gated channels affect visual information conveyed through the vertebrate retina.