Photoreceptor Physiology Group, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-2510.
Photoreceptor Physiology Group, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-2510
eNeuro. 2023 Nov 29;10(11). doi: 10.1523/ENEURO.0390-23.2023. Print 2023 Nov.
The detection of a single photon by a rod photoreceptor is limited by two sources of physiological noise, called discrete and continuous noise. Discrete noise occurs as intermittent current deflections with a waveform very similar to that of the single-photon response to real light and is thought to be produced by spontaneous activation of rhodopsin. Continuous noise occurs as random and continuous fluctuations in outer-segment current and is usually attributed to some intermediate in the phototransduction cascade. To confirm the origin of these noise sources, we have recorded from retinas of mouse lines with rods having reduced levels of rhodopsin, transducin, or phosphodiesterase. We show that the rate of discrete noise is diminished in proportion to the decrease in rhodopsin concentration, and that continuous noise is independent of transducin concentration but clearly elevated when the level of phosphodiesterase is reduced. Our experiments provide new molecular evidence that discrete noise is indeed produced by rhodopsin itself, and that continuous noise is generated by spontaneous activation of phosphodiesterase resulting in random fluctuations in outer-segment current.
杆状光感受器对单个光子的检测受到两种生理噪声源的限制，分别称为离散噪声和连续噪声。离散噪声以与真实光的单光子响应非常相似的波形间歇性地出现，被认为是由视紫红质的自发激活产生的。连续噪声则表现为外段电流的随机和连续波动，通常归因于光转导级联中的某个中间产物。为了确认这些噪声源的起源，我们从具有减少的视紫红质、转导蛋白或磷酸二酯酶水平的小鼠品系的视网膜中进行了记录。我们表明，离散噪声的速率与视紫红质浓度的降低成比例地减小，而连续噪声与转导蛋白浓度无关，但当磷酸二酯酶水平降低时，其明显升高。我们的实验提供了新的分子证据，表明离散噪声确实是由视紫红质本身产生的，而连续噪声是由磷酸二酯酶的自发激活导致外段电流随机波动而产生的。
