Molecular Mechanisms Characterizing Cone Photoresponses^†

Abstract

In the vertebrate retina, rods mediate twilight vision and cones mediate daylight vision. Their photoresponse characteristics are different. The light-sensitivity of a cone is 10 2 -10 3 times lower than that of a rod. In addition, the photoresponse time course is much faster in cones. The mechanism characterizing cone photoresponses has not been known mainly because of the difficulty in isolating cones in large quantities to perform biochemistry. Recently, we developed a method to purify cones from carp retina using a density gradient, which made it possible to analyze the differences in the molecular mechanism of phototransduction between rods and cones. The results showed that signal amplification in cones is less effective, which explains the lower light-sensitivity of cones. The results also showed that visual pigment phosphorylation, a quenching mechanism of lightactivated visual pigment, is much more rapid in cones than in rods. The rapid phosphorylation in cones is attributed to a very high total kinase activity in cones. Because of this high activity, cone pigment is readily phosphorylated even at very high bleaching levels, which probably explains why cone photoresponses recover quickly. Based on these findings, the molecular mechanisms of the differences in the photoresponse characteristics between rods and cones are outlined.

Phototransduction in mouse rods and cones

“…Interestingly, GRK7 was shown to have considerably higher specific activity than GRK1 and, is present at a much higher concentration in cones than GRK1 is in rods in fish [121,124]. This difference has been proposed as a potential mechanism underlying the faster shutoff and lower sensitivity of cones than rods (recently reviewed in [125]). …”

Highly efficient retinal metabolism in cones

“…This pathway of retinal processing (visual cycle) has been mainly studied in rods or rod-dominant retinas (3,4). Because cones function under much brighter light conditions, the visual cycle for cones could differ from that for rods in a qualitative and/or quantitative way, as is seen in the phototransduction mechanism in rods and cones (5,6).…”

Integration of a luminescent solar concentrator: Effects on daylight, correlated color temperature, illuminance level and color rendering index

“…The sensitivity of human vision system is connected to the wavelength of light (Tachibanaki et al, 2007;Petrides and Trexler, 2008;Fekete et al, 2010), and the spectral eye sensitivity curve Vk has the peak wavelength at 555 nm. The wavelength and color of the light regulates biological effects of the light-darkness cycle too Hattar et al, 2002;Bellia et al, 2011;Dacey et al, 2005) influencing a large variety of bodily processes (Gamlin et al, 2007;Van Bommel, 2006) and playing an important role in governing alertness, sleep and therefore wellness (Morita et al, 2003;Webb, 2006).…”