Pepperberg D R, Kahlert M, Krause A, Hofmann K P
Institut für Biophysik und Strahlenbiologie, Albert-Ludwigs Universität, Freiburg, Federal Republic of Germany.
Proc Natl Acad Sci U S A. 1988 Aug;85(15):5531-5. doi: 10.1073/pnas.85.15.5531.
On stimulation by green flashes, the isolated, aspartate-treated bovine retina exhibits transient changes in the scattering of near-infrared (880 nm) light. A single component, termed the "ATR" (a flash-induced scattering signal, where ATR designates amplified transient-retina), dominates the amplitude and rising-phase kinetics of the initial peak of the light-scattering response. Superfusion with physiological solution containing low Na+ concentration reversibly abolishes the photoreceptor electroretinographic response but preserves the ATR signal, indicating a receptoral origin for the ATR. The increase of ATR amplitude (A/Amax) with flash intensity (R*/R, where R indicates rhodopsin) is described by A/Amax = (1- e-kR*/R), with R*/R = k-1 occurring on generation of approximately two photoactivated rhodopsins (Rs) per disc surface in the rod outer segment. Weak background light and bright flashes reversibly depress the ATR. Kinetic and sensitivity data suggest a basis of the ATR in stochastic, unit activation events, each initiated by a single R. They further suggest an essential invariance of the unit event under differing conditions of illumination. A delay, apparently governed by the lifetime of a light-activated substance regulating ATR generation, precedes ATR recovery after a bright flash. The flash dependence of the delay period indicates an upper limit of 3 s for the lifetime of R* in the ATR-generating process. The unit event appears to be an R*-catalyzed and disc-localized reaction of phototransduction.
在绿色闪光刺激下，经天冬氨酸处理的离体牛视网膜在近红外（880纳米）光散射方面呈现出瞬时变化。一种单一成分，称为“ATR”（闪光诱导散射信号，其中ATR表示放大的瞬时视网膜），主导着光散射响应初始峰值的幅度和上升相动力学。用含低钠浓度的生理溶液进行灌流可使光感受器视网膜电图反应可逆性消失，但保留ATR信号，这表明ATR起源于感受器。ATR幅度（A/Amax）随闪光强度（R*/R，其中R表示视紫红质）的增加可用A/Amax = (1 - e-kR*/R)来描述，当在视杆外段每个盘膜表面产生约两个光活化视紫红质（R*）时，R*/R = k-1。弱背景光和强光闪光可使ATR可逆性降低。动力学和敏感性数据表明ATR基于随机的单位激活事件，每个事件由单个R引发。这些数据还表明在不同光照条件下单位事件具有基本不变性。在强光闪光后，ATR恢复之前存在一个延迟，该延迟显然受调节ATR产生的光活化物质寿命的控制。延迟期对闪光的依赖性表明在ATR产生过程中R的寿命上限为3秒。单位事件似乎是光转导中由R*催化且局限于盘膜的反应。
