How photons start vision
How photons start vision
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DOI：
10.1073/pnas.93.2.560
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发表时间：
1996-01-23
影响因子：
11.1
通讯作者：
Baylor, D
中科院分区：
文献类型：
--
作者：
Baylor, D
近期研究已经阐明，视杆细胞或视锥细胞吸收一个光子如何导致产生放大的神经信号，并将其传递给更高级的视觉神经元。光激发的视色素激活GTP结合蛋白——转导素，转导素进而刺激环鸟苷酸磷酸二酯酶。这种酶水解环鸟苷酸，使得细胞膜表面的环鸟苷酸门控阳离子通道关闭，使细胞超极化，并调节突触末端的递质释放。环鸟苷酸级联反应的动力学限制了整个视觉系统的时间分辨率，而反应中的统计波动限制了对微弱光线检测的可靠性。现在，很多研究兴趣集中在终止光反应以及动态调节级联放大的过程上，这些过程使得单光子反应具有可重复性，并使细胞能够适应背景光。内部游离钙离子浓度因光诱导而下降，协调了对放大作用的负反馈控制。钙离子浓度的下降刺激环鸟苷酸的重新合成，拮抗视紫红质的催化活性，并增加光调节阳离子通道对环鸟苷酸的亲和力。我们正在使用生理学方法研究终止闪光反应和介导适应的分子机制。一种方法是观察内部钙离子和核苷酸浓度受实验控制且可添加外源蛋白质的截短的、透析过的光感受器细胞中的转导过程。另一种方法是观察级联反应中特定蛋白质被改变或缺失的转基因小鼠视杆细胞中的转导过程。
Recent studies have elucidated how the absorption of a photon in a rod or cone cell leads to the generation of the amplified neural signal that is transmitted to higher-order visual neurons, Photoexcited visual pigment activates the GTP-binding protein transducin, which in turn stimulates cGMP phosphodiesterase. This enzyme hydrolyzes cGMP, allowing cGMP-gated cationic channels in the surface membrane to close, hyperpolarize the cell, and modulate transmitter release at the synaptic terminal, The kinetics of reactions in the cGMP cascade limit the temporal resolution of the visual system as a whole, while statistical fluctuations in the reactions limit the reliability of detection of dim light, Much interest now focuses on the processes that terminate the light response and dynamically regulate amplification in the cascade, causing the single photon response to be reproducible and allowing the cell to adapt in background light. A light-induced fall in the internal free Ca2+ concentration coordinates negative feedback control of amplification, The fall in Ca2+ stimulates resynthesis of cGMP, antagonizes rhodopsin's catalytic activity, and increases the affinity of the light-regulated cationic channel for cGMP, We are using physiological methods to study the molecular mechanisms that terminate the flash response and mediate adaptation. One approach is to observe transduction in truncated, dialyzed photoreceptor cells whose internal Ca2+ and nucleotide concentrations are under experimental control and to which exogenous proteins can be added. Another approach is to observe transduction in transgenic mouse rods in which specific proteins within the cascade are altered or deleted.