FEEDBACK REGULATION OF THE RETINAL ROD LIGHT RESPONSE

在视网膜杆中，入射光触发高度放大的酶 级联反应，导致环GMP激活通道关闭， 质膜。光转导级联的增益由下式设定： 环境光水平。在黑暗中，视网膜杆可以检测到一个单一的 光子，但其动态范围有限。的存在 然而，背景光会使视杆变得不敏感， 其动态范围。这一过程被称为光适应， 杆的能力，以检测对比度在一个广泛的光强度。 在本申请中，我们提出研究反馈机制， 通过降低耦合效率而有助于光适应 在光刺激和细胞反应之间。 尽管严格调控的光转导级联的许多步骤是 负责光的反馈机制的潜在目标 适应，这项建议的重点是两个最近发现的机制 它们似乎特别适合在这个过程中发挥作用。第一、 cGMP特异性磷酸二酯酶（PDE γ）的抑制亚基 以活性依赖的方式磷酸化;这种磷酸化 可能通过转导素阻断PDE催化活性的激活，G- 视网膜杆蛋白。第二，cGMP激活的抗体的亲和力， cGMP通道由过渡金属二价结合调节 阳离子和钙-钙调蛋白复合物。这些机制可能 增强或减弱cGMP水解与通道之间的耦合 结束负责这两个过程的分子机制 将使用一种方法研究它们对光适应的贡献 生物化学、分子生物学和电生理学的组合 方法. 这些实验将增加我们对视网膜杆如何 产生一个神经信号，以响应入射光子，以及如何杆可以 改变他们的行为以应对不断变化的刺激。更深 对视网膜视杆细胞功能的了解将为 治疗视网膜色素变性和夜盲症。 此外，由于视网膜杆利用共同的信号机制， 这项研究还应该提供对信号调节的深入了解， 整个身体的传导途径。

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.