BIOPHYSICAL MECHANISMS OF SINGLE PHOTON DETECTION

单光子检测的生物物理机制

• 批准号: 2372539
• 负责人: FREDERICK M RIEKE
• 金额: $ 18.79万
• 依托单位: UNIVERSITY OF WASHINGTON
• 依托单位国家: 美国
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-08-01 至 2001-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/2372539
• 关键词: Urodela; behavioral /social science research tag; calcium flux; calcium indicator; chemical kinetics; electrophysiology; neural transmission; retina; retinal adaptation; retinal bipolar neuron; rhodopsin; rod cell; single cell analysis; synapses; tissue /cell culture; toad; visual perception; visual photosensitivity; visual phototransduction

DESCRIPTION (Adapted from applicant's abstract): The ability of the dark-adapted visual system to count photon absorptions has been known for many years; however, the biophysical mechanisms which make photon detection and counting possible are not understood. Much of rod vision occurs at light levels where photon absorptions occur rarely; thus, failure of these biophysical processes will severely impair rod vision. The reliability of photon counting means that the transduction process in the rod outer segment must produce distinguishable responses to absorption of O, 1, or 2 photons, and that these signals are reliably transmitted from the rod to the rest of the visual system. Current understanding of signal transduction and synaptic transmission cannot account for this level of performance. Experiments proposed here will determine the mechanisms mediating reliable transduction of single photon absorptions and reliable transmission of these responses to second order cells. Studies of phototransduction will determine how each absorbed photon produces a nearly identical current response. This reproducibility is essential for reliable photon counting, but is surprising given the expected statistical fluctuations in the small number of molecules involved, particularly in the shutoff of photoexcited rhodopsin. Elements of the transduction cascade will be selectively altered to determine if they are necessary for reproducible single photon responses. Studies of synaptic transmission will determine how single photon responses are reliably transmitted to second order cells in the retina, and how pre-synaptic mechanisms separate light signals from photoreceptor noise. The single photon signal traversing the synapse and the noise generated in synaptic transmission will be studied by monitoring the post-synaptic current in a bipolar cell while controlling the rod voltage. Signal transfer to bipolar cells also separates light signals from photoreceptor noise. A likely mechanism mediating this synaptic filtering is the control of the Ca2+ concentration in the synaptic terminal. To test this idea, the kinetics of Ca2+ changes in the terminal will be measured with fluorescent indicators and compared to the kinetics of signal transfer. A further test will be made by determining how the kinetics of signal transfer are altered when the buffering capacity of the terminal is changed.

描述（改编自申请人的摘要）： 用于计算光子吸收的暗适应视觉系统因 许多年；然而，使光子检测的生物物理机制 和可能的计数不被理解。 杆状视觉的大部分发生在 很少发生光子吸收的光水平；因此，这些失败 生物物理过程会严重损害视杆细胞的视力。 可靠性 光子计数意味着杆外段的转导过程 必须对 O、1 或 2 个光子的吸收产生可区分的响应， 并且这些信号可靠地从杆传输到其余部分 视觉系统。 目前对信号转导的理解 突触传递无法解释这种性能水平。 这里提出的实验将确定调解可靠的机制 单光子吸收的传导和这些的可靠传输 对二阶细胞的反应。 光转导研究将确定每个光子如何吸收 产生几乎相同的电流响应。 这个再现性是 对于可靠的光子计数至关重要，但考虑到预期的结果，这令人惊讶 所涉及的少量分子的统计波动， 特别是在光激发视紫红质的关闭方面。 的要素 将选择性地改变转导级联以确定它们是否是 可重复的单光子响应所必需的。 突触传递的研究将确定单光子如何响应 可靠地传输到视网膜的二级细胞，以及如何 突触前机制将光信号与感光器噪声分开。 穿过突触的单光子信号和产生的噪声 通过监测突触后信号来研究突触传递 双极电池中的电流，同时控制棒电压。 信号 转移到双极细胞也将光信号与感光器分离 噪音。 介导这种突触过滤的一种可能机制是控制 突触末端 Ca2+ 浓度。 为了测试这个想法， 末端 Ca2+ 变化的动力学将用荧光测量 指标并与信号传递动力学进行比较。 进一步测试 将通过确定如何改变信号传递的动力学来实现 当终端的缓冲能力改变时。