Department of Physiology, School of Medicine, University of California San Francisco, San Francisco, CA 94920, USA.
Prog Retin Eye Res. 2012 Sep;31(5):442-66. doi: 10.1016/j.preteyeres.2012.05.002. Epub 2012 May 29.
The light responses of rod and cone photoreceptors in the vertebrate retina are quantitatively different, yet extremely stable and reproducible because of the extraordinary regulation of the cascade of enzymatic reactions that link photon absorption and visual pigment excitation to the gating of cGMP-gated ion channels in the outer segment plasma membrane. While the molecular scheme of the phototransduction pathway is essentially the same in rods and cones, the enzymes and protein regulators that constitute the pathway are distinct. These enzymes and regulators can differ in the quantitative features of their functions or in concentration if their functions are similar or both can be true. The molecular identity and distinct function of the molecules of the transduction cascade in rods and cones are summarized. The functional significance of these molecular differences is examined with a mathematical model of the signal-transducing enzymatic cascade. Constrained by available electrophysiological, biochemical and biophysical data, the model simulates photocurrents that match well the electrical photoresponses measured in both rods and cones. Using simulation computed with the mathematical model, the time course of light-dependent changes in enzymatic activities and second messenger concentrations in non-mammalian rods and cones are compared side by side.
脊椎动物视网膜中的视杆和视锥光感受器的光反应在数量上有所不同，但由于将光吸收和视觉色素激发与外段质膜中的 cGMP 门控离子通道门控联系起来的酶促反应级联的非凡调节，它们非常稳定且可重现。虽然光转导途径的分子方案在视杆和视锥中基本相同，但构成途径的酶和蛋白调节剂是不同的。如果它们的功能相似，则这些酶和调节剂在功能的定量特征上可能存在差异，或者两者都可能是正确的。总结了光转导级联中视杆和视锥的分子的分子特征和独特功能。使用信号转导酶级联的数学模型检查了这些分子差异的功能意义。受可用的电生理学、生物化学和生物物理数据的限制，该模型模拟的光电流与在视杆和视锥中测量的电光反应非常吻合。使用数学模型进行的模拟计算，比较了非哺乳动物视杆和视锥中酶活性和第二信使浓度的光依赖性变化的时间过程。
