Kawakami Naoto, Kawamura Satoru
Graduate School of Frontier Biosciences, and.
Graduate School of Frontier Biosciences, and Department of Biological Sciences, Graduate School of Science, Osaka University, Yamada-oka 1-3, Suita, Osaka 565-0871, Japan
J Neurosci. 2014 Oct 29;34(44):14682-6. doi: 10.1523/JNEUROSCI.3389-14.2014.
In the vertebrate retina, there are two types of photoreceptors, rods and cones. Rods are highly light-sensitive and cones are less light-sensitive. One of the possible mechanisms accounting for the lower light-sensitivity in cones would be lower signal amplification, i.e., lower gain in the phototransduction cascade in cones. In this study, we compared the difference in the gain between rods and cones electrophysiologically in carp. The initial rising phases of the light responses were analyzed to determine an index of the gain, G, a parameter that can be used to compare the gain among cells of varying outer segment volumes. G (in fL · sec(-2)) was 91.2 ± 14.8 (n = 5) in carp rods and 25.3 ± 3.2 (n = 4) in carp red cones, so that the gain in carp red cones is ∼1/4 of that in carp rods. G was also determined in bullfrog rods and was 81.0 ± 17.2 (n = 3) which was very similar to that in carp rods. The difference in the gain between rods and cones in carp determined in this study (∼1/4 in cones compared with rods) is consistent with that we recently determined biochemically (∼1/5 in cones compared with rods). Together with the result obtained in bullfrog rods in this study and the results obtained by others, we concluded that the gain in the cascade is several-fold lower in cones than in rods in carp and probably in other animal species also.
在脊椎动物视网膜中，存在两种光感受器，即视杆细胞和视锥细胞。视杆细胞对光高度敏感，而视锥细胞对光的敏感度较低。视锥细胞光敏感度较低的一种可能机制是信号放大较低，即在视锥细胞的光转导级联反应中增益较低。在本研究中，我们通过电生理方法比较了鲤鱼视杆细胞和视锥细胞之间增益的差异。分析光反应的初始上升阶段以确定增益指数G，该参数可用于比较不同外段体积细胞之间的增益。鲤鱼视杆细胞的G（单位为fL·sec(-2)）为91.2±14.8（n = 5），鲤鱼红色视锥细胞的G为25.3±3.2（n = 4），因此鲤鱼红色视锥细胞的增益约为鲤鱼视杆细胞增益的1/4。我们还测定了牛蛙视杆细胞的G，其值为81.0±17.2（n = 3），与鲤鱼视杆细胞的G非常相似。本研究中测定的鲤鱼视杆细胞和视锥细胞之间的增益差异（视锥细胞与视杆细胞相比约为1/4）与我们最近通过生化方法测定的结果（视锥细胞与视杆细胞相比约为1/5）一致。结合本研究中牛蛙视杆细胞获得的结果以及其他研究人员获得的结果，我们得出结论，在鲤鱼以及可能在其他动物物种中，视锥细胞级联反应中的增益比视杆细胞低几倍。
