In the vertebrate retina, rods and cones both detect light, but they differ in functional aspects such as light sensitivity and temporal resolution, and in some cell biological aspects. For functional aspects, both types of photoreceptors use a phototransduction cascade, consisting of a series of enzymatic reactions, to convert photon capture to an electrical signal. To understand the mechanisms underlying the functional differences between rods and cones at the molecular level, we compared biochemically, each of the reactions in the phototransduction cascades of rods and cones using the cells isolated and purified from carp retina.

Although the cascade proteins are identical or are functionally similar between rods and cones, their activities together with their expression levels are mostly different. In general, reactions that generate a response are somewhat less effective in cones than in rods, but each of the reactions for termination and recovery of a response are much more effective in cones. These findings explain lower light sensitivity and briefer light responses in cones than in rods. In addition, our considerations suggest that a Ca²⁺-binding protein, S-modulin or recoverin, has a currently unnoticed role in shaping light responses.

Upon comparison of the expression levels of proteins and/or mRNAs using purified cells, several proteins were found to be specifically or predominantly expressed in cones. These proteins will be of interest in future studies aimed at characterizing the differences between rods and cones.

在脊椎动物的视网膜中，视杆细胞和视锥细胞都可以检测光，但它们在功能方面（例如光敏感性和时间分辨率）以及某些细胞生物学方面有所不同。在功能方面，两种类型的感光器都使用由一系列酶促反应组成的光转导级联，将光子捕获转换为电信号。为了在分子水平上了解视杆细胞和视锥细胞之间功能差异的潜在机制，我们使用从鲤鱼视网膜中分离和纯化的细胞，对视杆细胞和视锥细胞的光转导级联中的每个反应进行了生化比较。

尽管视杆细胞和视锥细胞之间的级联蛋白相同或功能相似，但它们的活性及其表达水平大多不同。一般来说，产生响应的反应在视锥细胞中的效果比在视锥细胞中的效果要差一些，但每个用于终止和恢复响应的反应在视锥细胞中都更有效。这些发现解释了视锥细胞的光敏感度低于视杆细胞，光响应更短。此外，我们的考虑表明，Ca ²⁺结合蛋白、S-调节蛋白或恢复素在塑造光响应方面具有目前未被注意到的作用。

在使用纯化细胞比较蛋白质和/或 mRNA 的表达水平后，发现几种蛋白质在视锥细胞中特异性或主要表达。这些蛋白质将在未来旨在表征视杆细胞和视锥细胞之间差异的研究中引起关注。