NMDA modulates sodium and calcium retinal channels

描述(申请人提供)：这项建议旨在表征NMDA对视网膜水平细胞电压门控钠和钙电流的调制，探索调制发生的机制，并研究NMDA在视网膜远端的功能含义。NMDA受体在大脑中的作用与长时程增强、兴奋毒性、神经发育和可塑性有关，已被广泛研究。然而，在远端视网膜中，NMDA受体的作用尚不清楚。根据初步数据，将被测试的模型是，水平细胞中NMDA受体的激活导致钙通过NMDA通道和CICR从对咖啡因敏感的细胞内存储中流入。NMDA对电压敏感的钠和钙电导的抑制依赖于这一点和钙结合蛋白钙调蛋白的激活。 光反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明暗条件有关的细节。因此，在临床开发足够的人造视网膜之前，以及在影响视网膜的疾病(如帕金森氏症)的治疗有效之前，了解电压门控通道如何对这种视觉信息进行编码是至关重要的。这一建议中概述的三个具体目标旨在：i)检验NMDA受体激活既抑制电压门控钠电流又抑制电压门控钙电流的假说；ii)检验NMDA参与形成视锥水平细胞的光反应和暗静息膜电位的假说；iii)检验钙依赖的信号通路将NMDA受体的激活与抑制视锥水平细胞的电压门控钠通道和钙通道联系起来的假说。这些具体目标将使用结合电生理学、药理学、免疫细胞化学和钙成像技术的多学科方法来实现。使用分离细胞和视网膜切片制备获得的结果将大大有助于这项研究的长期目标，即了解电压门控通道如何影响通过脊椎动物视网膜传达的视觉信息。

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.