■光检测会破坏视觉色素。它的再生,光灵敏度的恢复所必需的,是通过视觉周期完成的。通过光活化的视觉色素释放全反式视黄醛并将其还原成全反式视黄醇包括视觉周期的第一步。在这项研究中,我们确定了人视杆和视锥光感受器中全反式视黄醇形成的动力学。
■从人类尸体眼(年龄21至90岁)的视网膜中分离出单个活杆和视锥光感受器。全反式视黄醇的形成通过成像其外段荧光(激发,360nm;发射,>420nm)。通过测量340和380nm激发的荧光来确定释放的全反式视黄醛向全反式视黄醇的转化程度。用从猕猴视网膜分离的光感受器重复测量。实验在37℃下进行。
■我们发现,光活化色素释放的80%至90%的全反式视黄醛转化为全反式视黄醇,在人类视杆中的速率常数为0.24至0.55min-1,在人类视锥中的速率常数为1.8min-1。在M.fascicularis杆和锥中,速率常数分别为0.38±0.08min-1和4.0±1.1min-1。这些动力学比在其他脊椎动物中测量的动力学快几倍。光感受器间类视黄醇结合蛋白有助于从人杆中去除全反式视黄醇。
■人类光感受器的视觉周期的第一步比其他脊椎动物快几倍,并且与人类视觉系统表现出的光敏性的快速恢复相一致。
UNASSIGNED: Light detection destroys the visual pigment. Its regeneration, necessary for the recovery of light sensitivity, is accomplished through the visual cycle. Release of all-trans retinal by the light-activated visual pigment and its reduction to all-trans retinol comprise the first steps of the visual cycle. In this study, we determined the kinetics of all-trans retinol formation in human rod and cone photoreceptors.
UNASSIGNED: Single living rod and cone photoreceptors were isolated from the retinas of human cadaver eyes (ages 21 to 90 years). Formation of all-trans retinol was measured by imaging its outer segment fluorescence (excitation, 360 nm; emission, >420 nm). The extent of conversion of released all-trans retinal to all-trans retinol was determined by measuring the fluorescence excited by 340 and 380 nm. Measurements were repeated with photoreceptors isolated from Macaca fascicularis retinas. Experiments were carried out at 37°C.
UNASSIGNED: We found that ∼80% to 90% of all-trans retinal released by the light-activated pigment is converted to all-trans retinol, with a rate constant of 0.24 to 0.55 min-1 in human rods and ∼1.8 min-1 in human cones. In M. fascicularis rods and cones, the rate constants were 0.38 ± 0.08 min-1 and 4.0 ± 1.1 min-1, respectively. These kinetics are several times faster than those measured in other vertebrates. Interphotoreceptor retinoid-binding protein facilitated the removal of all-trans retinol from human rods.
UNASSIGNED: The first steps of the visual cycle in human photoreceptors are several times faster than in other vertebrates and in line with the rapid recovery of light sensitivity exhibited by the human visual system.