Role of visual pigment properties in rod and cone phototransduction

Vladimir Kefalov, Yingbin Fu, Nicholas Marsh-Armstrong and King-Wai Yau ()
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Vladimir Kefalov: Johns Hopkins University School of Medicine
Yingbin Fu: Johns Hopkins University School of Medicine
Nicholas Marsh-Armstrong: Johns Hopkins University School of Medicine
King-Wai Yau: Johns Hopkins University School of Medicine

Nature, 2003, vol. 425, issue 6957, 526-531

Abstract: Abstract Retinal rods and cones share a phototransduction pathway involving cyclic GMP1. Cones are typically 100 times less photosensitive than rods and their response kinetics are several times faster2, but the underlying mechanisms remain largely unknown. Almost all proteins involved in phototransduction have distinct rod and cone variants. Differences in properties between rod and cone pigments have been described, such as a 10-fold shorter lifetime of the meta-II state (active conformation) of cone pigment3,4,5,6 and its higher rate of spontaneous isomerization7,8, but their contributions to the functional differences between rods and cones remain speculative. We have addressed this question by expressing human or salamander red cone pigment in Xenopus rods, and human rod pigment in Xenopus cones. Here we show that rod and cone pigments when present in the same cell produce light responses with identical amplification and kinetics, thereby ruling out any difference in their signalling properties. However, red cone pigment isomerizes spontaneously 10,000 times more frequently than rod pigment. This high spontaneous activity adapts the native cones even in darkness, making them less sensitive and kinetically faster than rods. Nevertheless, additional factors are probably involved in these differences.

Date: 2003
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DOI: 10.1038/nature01992

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