BIOPHYSICAL MECHANISMS OF SINGLE PHOTON DETECTION

单光子检测的生物物理机制

• 批准号: 2888575
• 负责人: FREDERICK M RIEKE
• 金额: $ 16.86万
• 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/2888575
• 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（改编自申请人摘要）： 一种用于计算光子反射的暗适应视觉系统， 许多年;然而，使光子探测的生物物理机制 和计数可能不被理解。 大部分视杆细胞的视力出现在 光水平，光子反射很少发生;因此，这些 生物物理过程将严重损害视杆视觉。 的可靠性 光子计数意味着杆外节中的转导过程 必须对0、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杆的其余部分， 视觉系统。 目前对信号转导和 突触传递不能解释这种水平的性能。 这里提出的实验将确定中介可靠的机制 单光子激发的转换和这些激发的可靠传输 对二阶细胞的反应。 光传导的研究将确定每个吸收的光子 产生几乎相同的电流响应。 这种再现性是 这对于可靠的光子计数至关重要，但考虑到预期的 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阻断中。 要素 转导级联将被选择性地改变以确定它们是否是 对于可再现的单光子响应是必要的。 对突触传递的研究将确定单光子如何响应 可靠地传递到视网膜的二级细胞，以及如何传递到视网膜的二级细胞， 突触前机制将光信号与光感受器噪声分开。 穿过突触的单光子信号和在突触中产生的噪声， 突触传递将通过监测突触后 电流在双极电池，同时控制棒电压。 信号 转移到双极细胞也将光信号从光感受器分离 噪声 调节这种突触过滤的可能机制是控制 突触末梢的Ca 2+浓度。 为了验证这个想法， 末端中Ca 2+变化的动力学将用荧光光谱法测量。 指标，并与信号传递的动力学进行比较。 另一测试 将通过确定信号传递的动力学如何改变来进行 当终端的缓冲容量改变时。