title: Rhodopsin in the rod surface membrane regenerates more rapidly than bulk rhodopsin in the disc membranes in vivo.
abstract: Sustained vertebrate vision requires that opsin chromophores isomerized by light to the all-trans form be replaced with 11-cis retinal to regenerate the visual pigment. We have characterized the early receptor potential (ERP), a component of the electroretinogram arising from photoisomerization-induced charge displacements in plasma membrane visual pigment, and used it to measure pigment bleaching and regeneration in living mice. The mouse ERP was characterized by an outward 'R2' charge displacement with a time constant of 215 μs that discharged through a membrane with an apparent time constant of ∼0.6 ms. After complete bleaching of rhodopsin, the ERP recovered in two phases. The initial, faster phase had a time constant of ∼1 min, accounted for ∼20% of the total, and was not dependent on the level of expression of the retinal pigment epithelium isomerase, Rpe65. The slower, complementary phase had a time constant of 23 min in wild-type (WT) mice (C57Bl/6) and was substantially slowed in Rpe65(+/-) mice. Comparison of the ERPs of a mouse line expressing 150% of the normal level of cone M-opsin with those of WT mice revealed that M-opsin contributed 26% of the total WT ERP in these experiments, with the remaining 74% arising from rhodopsin. Thus, the fast regenerating fraction (20%) corresponds approximately to the fraction of the total ERP independently estimated to arise from M-opsin. Because both phases of the ERP recover substantially faster than previous measurements of bulk rhodopsin regeneration in living mice, we conclude that delivery of the highly hydrophobic 11-cis retinal to the interior of rod photoreceptors appears to be retarded by transit across the cytoplasmic gap between plasma and disc membranes.
authors.affiliation: Center for Neuroscience, University of California, Davis, Davis, CA, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Kessler
authors.affiliation: Center for Neuroscience, University of California, Davis, Davis, CA, USA.
authors.forename: Megan
authors.initials: M
authors.lastname: Tillman
authors.affiliation: Department of Ophthalmology and Vision Science, University of California, Davis, Davis, CA, USA Department of Cell Biology and Human Anatomy, University of California, Davis, Davis, CA, USA.
authors.forename: Marie E
authors.initials: ME
authors.lastname: Burns
authors.affiliation: Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, USA Department of Cell Biology and Human Anatomy, University of California, Davis, Davis, CA, USA enpugh@ucdavis.edu.
authors.forename: Edward N
authors.initials: EN
authors.lastname: Pugh
mesh_terms: D000200:Action Potentials; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D055358:Cone Opsins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D021381:Protein Transport; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism* / Q000502:physiology; D012243:Rhodopsin / Q000378:metabolism*; D019745:cis-trans-Isomerases / Q000378:metabolism; D000099178:Retinoid Isomerohydrolase
chemical_list: D055358:Cone Opsins; D012243:Rhodopsin; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase