Larger inhibition of visual pigment kinase in cones than in rods

Abstract

J. Neurochem. (2010) 115, 259–268. Abstract In the carp retina, visual pigment kinase, GRK1 (G‐protein coupled receptor kinase 1) in rods and GRK7 in cones, is inhibited by a photoreceptor neuronal Ca2+‐sensor protein, S‐modulin (or recoverin) in rods and visinin (formerly named s26) in cones. Here, we compared Ca2+‐dependent inhibition of GRK1 by S‐modulin and that of GRK7 by visinin. First, the concentrations of S‐modulin and visinin in the outer segment were estimated: the concentration of visinin (1.2 mM) was 20 times higher than that of S‐modulin (53 μM). Based on the determined concentrations of the Ca2+‐sensor proteins and the known dark Ca2+ concentrations, we estimated that in situ Ca2+‐dependent inhibition on GRK in cones would be 2.5 times higher than that in rods at the Ca2+ concentration in the dark. Because GRK activity is approximately 100 times higher in cones than in rods [Proc. Natl Acad. Sci. USA102 (2005) 21359], the range of Ca2+‐dependent inhibition on GRK activity is more than 100 times wider in cones than in rods. The inhibitory effects of S‐modulin and visinin on photoreceptor GRKs were indistinguishable, although these Ca2+‐sensor proteins are expressed in a cell‐type specific manner. The inhibition by these Ca2+‐sensor proteins was slightly higher on GRK7 than GRK1 probably because of a characteristic specific to GRK7.

Regulation of Mammalian Cone Phototransduction by Recoverin and Rhodopsin Kinase

“…However, one notable difference was the acceleration of the time to peak of the dim flash response in cones ( Tables 1 and 2) that was not observed in rods (10). This result is consistent with a recent study from carp retina that found stronger inhibition of GRK7 in cones compared with GRK1 in rods (39) and suggests that under dim light conditions, recoverin might play a more dominant role in phototransduction inactivation in cones compared with rods.…”

“…Fish and amphibian photoreceptors use two separate calcium modulators of rhodopsin kinase: recoverin (or S-modulin) in rods (8,27) and visinin in cones (38). Notably, the expression of the corresponding calcium modulator of GRK is estimated to be 20 times higher in cones compared with rods (39). Furthermore, the same study found that recoverin is 2-fold more abundant than GRK1 in the outer segments of carp rods, whereas visinin is 5-fold more abundant than the corresponding level of cone opsin kinase (GRK7) in carp cones.…”

“…Finally, it is intriguing that increasing GRK1 levels in cones reduce their recoverin/GRK ratio toward its rod value (39) while at the same time tend to slow down their flash responses, also toward their rod values. The dichotomy of the effects of GRK1 expression in rods and cones reveals a level of complexity of their respective phototransduction cascades that has not been previously appreciated.…”

Phosphorylation-independent Suppression of Light-activated Visual Pigment by Arrestin in Carp Rods and Cones

“…Immunofluorescent Staining of OS-IS Cells-Immunofluorescent staining of OS-IS rods and cones was performed as described (19). Carp rods and cones were obtained in the dark with a simplified purification method by using a stepwise Percoll density gradient consisting of 30 and 90% Percoll in the presence of 4% (w/v) paraformaldehyde.…”

Regulation of calcium homeostasis in the outer segments of rod and cone photoreceptors

“…In rods, the recoverin-mediated suppression of pigment inactivation delays the flash response recovery under dim light when [Ca 2+ ] i is high, but has little effect on sensitivity during light adaptation when [Ca 2+ ] i declines (Makino et al, 2004). Notably, the expression of the corresponding calcium modulator of rhodopsin kinase is estimated to be 20 times higher in cones compared to rods (Arinobu et al, 2010). In addition, calcium had been shown to modulate the sites and extent of pigment phosphorylation in zebrafish cones but not in rods (Kennedy et al, 2004).…”