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Keisuke Sakurai, Shahrokh C. Khani, Vladimir J. Kefalov; Effect Of G-protein Coupled Kinase 1 Expression On Mouse Cone Photoresponse Termination. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5262.
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G-protein coupled receptor kinase 1 (GRK1) is responsible for the phosphorylation of photo activated pigments and the timely response inactivation in both mouse rods and cone photoreceptors. However it is not known whether the expression level of GRK1 modulates cone photoresponse recovery. To address this question, we investigated recovery of photoresponse using transgenic mice with varying GRK1 expression in whole retina.
Transretinal electroretinogram (ERG) a-wave recordings were carried out using a mouse retina expressing GRK1 at normal (wild type), 0.3- (GRK1+/-) or 3-fold (GRK1+) the wild-type level. Transretinal ERG recordings were done from dorsal mouse retina, with synaptic transmission inhibited pharmacologically to isolate the photoreceptor flash response. To remove the rod component of the whole retina flash responses, all recordings were done from mice in rod transducin alpha knockout (Gnat1-/-) background.
We found that, surprisingly, the shutoff of cone dim flash responses slowed down with increasing expression of GRK1. Thus, their time to peak increased from 93 ± 4 ms (n = 5) in GRK1+/- cones, to 135 ± 7 ms (n = 9) in wild type, and to 152 ± 5 ms (n=6) in GRK1+ cones. In addition, the integration time, Tint, was significantly prolonged from 112 ± 21 ms in GRK1+/- cones, to 293 ± 28 ms in wild type, and to 426 ± 19 ms for Grk1+ cones. The saturated cone response amplitude also increased with increasing GRK1 expression level, from 10.1µV for GRK+/- retina, to 15.6 µV for wild type, and to 19.0 µV for GRK+ retina. Interestingly, responses to flashes bleaching more than 1% cone pigments had uniform kinetics independent of GRK1 expression level.
Surprisingly, in contrast to rods, upregulation of GRK1expression level in cones prolongs their dim flash response. In contrast, for brighter light the shutoff of the cone photoresponse was independent of the level of GRK1expression. Thus, GRK1 modulates response shutoff in cones differently than in rods under dim light conditions. Under brighter light, cone response appears not to be regulated by GRK1 expression levels.
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