The interphotoreceptor retinoid binding (IRBP) is essential for normal retinoid processing in cone photoreceptors.
11-cis Retinal is the light-sensitive component in rod and cone photoreceptors, and its isomerization to all-trans retinal in the presence of light initiates the visual response. For photoreceptors to function normally, all-trans retinal must be converted back into 11-cis retinal through the visual cycle. While rods are primarily responsible for dim light vision, the ability of cones to function in constant light is essential to human vision and may be facilitated by cone-specific visual cycle pathways. The interphotoreceptor retinoid-binding protein (IRBP) is a proposed retinoid transporter in the visual cycle, but rods in Irbp ( -/- ) mice have a normal visual cycle. However, there is evidence that IRBP has cone-specific functions. Cone electroretinogram (ERG) responses are reduced, despite having cone densities and opsin levels similar to C57Bl/6 (WT) mice. Treatment with 9-cis retinal rescues the cone response in Irbp ( -/- ) mice and shows that retinoid deficiency underlies cone dysfunction. These data indicate that IRBP is essential to normal cone function and demonstrate that differences exist in the visual cycle of rods and cones.
Parker
Ryan O
RO
Department of Neurosciences, Medical University of South Carolina, Charleston, SC, USA. parkerry@musc.edu
Crouch
Rosalie K
RK
D000375:Aging / Q000378:metabolism; D000818:Animals; D004596:Electroretinography; D005136:Eye Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology / Q000378:metabolism*; D012176:Retinoids / Q000378:metabolism*; D012177:Retinol-Binding Proteins / Q000172:deficiency / Q000378:metabolism*; D014785:Vision, Ocular; D000099214:Retinol-Binding Proteins, Interstitial
D005136:Eye Proteins; D012176:Retinoids; D012177:Retinol-Binding Proteins; D000099214:Retinol-Binding Proteins, Interstitial