FEEDBACK REGULATION OF THE RETINAL ROD LIGHT RESPONSE

在视网膜棒中，入射光触发高度放大的酶 导致GMP激活的循环通道关闭的级联反应 质膜。光传导级联的增益由下式设置 环境光级别。在黑暗中，视网膜视杆可以检测到 光的光子，但其动态范围有限。.的存在 然而，背景光会使杆子变得不敏感，从而移动和伸展 它的动态范围。这个过程被称为光适应，最大化地 Rod在大范围的光强度范围内检测对比度的能力。 在本申请中，我们建议调查反馈机制，这些反馈机制可能 通过降低耦合效率来促进光适应 光刺激和细胞反应之间的关系。 尽管严格调控的光转导级联的许多步骤是 光反馈机制的潜在靶点 适应，这项建议侧重于最近发现的两种机制 它们似乎特别适合在这一过程中发挥作用。第一, CGMP特异性磷酸二酯酶抑制亚单位(PDEgamma) 以一种依赖于活性的方式磷酸化；这种磷酸化 可阻断转导蛋白对PDE催化活性的激活， 视网膜杆的蛋白质。第二，cGMP激活的亲和力 CGMP通道受过渡金属二价结合的调节 阳离子和钙-钙调蛋白复合体。这些机制可以是 加强或减弱cGMP水解酶与通道之间的耦合 结案了。负责这两个过程的分子机制 它们对光适应的贡献将通过一个 生物化学、分子生物学和电生理学的结合 方法：研究方法。 这些实验将增加我们对视网膜杆如何 产生神经信号以响应入射光子，以及杆子如何 改变他们的行为，以应对不断变化的刺激。更深一层的 对视网膜视杆功能的了解将为以后的研究奠定基础 治疗视网膜色素变性和夜盲症等疾病。 此外，由于视网膜杆利用共同的信号机制， 这项研究也应该提供对信号调节的洞察力 全身的转导通路。

In retinal rods, incident light triggers a highly amplified enzymatic cascade that results in the closure of cyclic GMP-activated channels in the plasma membrane. The gain of the phototransduction cascade is set by the ambient light level. In darkness, a retinal rod can detect a single photon of light, but its dynamic range is limited. The presence of background light, however, desensitizes the rod, shifting and extending its dynamic range. This process, known as light adaptation, maximizes the rod's ability to detect contrast over a broad range of light intensities. In this application we propose to investigate feedback mechanisms that may contribute to light adaptation by decreasing the efficiency of coupling between the light stimulus and the cellular response. Although many steps of the tightly regulated phototransduction cascade are potential targets for the feedback mechanisms responsible for light adaptation, this proposal focuses on two recently discovered mechanisms which seem particularly well-suited to play a role in this process. First, the inhibitory subunit of the cGMP-specific phosphodiesterase (PDEgamma) is phosphorylated in an activity-dependent manner; this phosphorylation may block activation of PDE catalytic activity by transducin, the G- protein of retinal rods. Second, the affinity of the cGMP-activated channels for cGMP is regulated by the binding of transition metal divalent cations and the calcium-calmodulin complex. These mechanisms may either strengthen or weaken the coupling between cGMP hydrolysis and channel closure. The molecular mechanisms responsible for both of these processes and their contribution to light adaptation will be studied using a combination of biochemical, molecular biological, and electrophysiological methods. These experiments will increase our understanding of how retinal rods generate a neural signal in response to incident photons, and how rods can modify their behavior in response to changing stimuli. A deeper understanding of retinal rod function will provide a foundation for the treatment of diseases like retinitis pigmentosa and night blindness. Furthermore, because retinal rods utilize common signaling mechanisms, this research should also provide insight into the regulation of signal transduction pathways throughout the body.