title: Interphotoreceptor retinoid-binding protein (IRBP) promotes retinol uptake and release by rat Müller cells (rMC-1) in vitro: implications for the cone visual cycle.
abstract: OBJECTIVE
  Interphotoreceptor retinoid-binding protein's (IRBP) role in facilitating the exchange of retinoids between rod and cone photoreceptors, RPE, and Müller cells in the visual cycle remains a mystery. Interphotoreceptor retinoid-binding protein's ability to bind the pericellular matrix of the cone outer segment and Müller cell villi suggests a function in all-trans and 11-cis retinol targeted trafficking in the cone visual cycle. We hypothesize that IRBP facilitates delivery and uptake of all-trans retinol to and release of 11-cis retinol from rat Müller cells (rMC-1).
  
  
  METHODS
  Rat Müller cells were incubated with all-trans retinol and BSA or bovine IRBP (bIRBP). Retinoids in the cell homogenates and conditioned media were analyzed by high performance liquid chromatography (HPLC).
  
  
  RESULTS
  Cells incubated with 10 μM retinol and BSA had 2100 pmol of all-trans retinol per milligram homogenate protein compared with 3450 pmol when retinol was delivered by bIRBP; these cells also had 450 pmol all-trans retinyl ester per milligram when retinol was delivered by BSA compared with 270 pmol when retinol was delivered by bIRBP. Conditioned media from cells incubated with retinol delivered by BSA did not contain11-cis retinol. However, cells with retinol delivered by bIRBP released 130 pmol/mL of 11-cis retinol into the cell media. Incubation with 5.0 mM deferoxamine (an iron chelator) reduced IRBP-dependent 11-cis retinol retrieval by 60%.
  
  
  CONCLUSIONS
  Promoting Müller cell uptake of all-trans retinol and release of 11-cis retinol is a previously unrecognized function of IRBP that may be critical to cone function and integrity.
authors.affiliation: Department of Biology, The University of Texas at San Antonio, San Antonio, Texas, United States.
authors.forename: Brandi S
authors.initials: BS
authors.lastname: Betts-Obregon
authors.affiliation: Medical Research Service, Veterans Affairs Medical Center, Buffalo, New York, New York, United States Departments of Ophthalmology (Ross Eye Institute) and Pathology & Anatomic Sciences; Graduate Program in Neurosciences, SUNY Eye Institute, State University of New York, Buffalo, New York, United States.
authors.forename: Federico
authors.initials: F
authors.lastname: Gonzalez-Fernandez
authors.affiliation: Department of Biology, The University of Texas at San Antonio, San Antonio, Texas, United States.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Tsin
mesh_terms: D000818:Animals; D002417:Cattle; D002452:Cell Count; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D016895:Culture Media, Serum-Free; D063928:Ependymoglial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism*; D051381:Rats; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012177:Retinol-Binding Proteins / Q000378:metabolism*; D014785:Vision, Ocular / Q000502:physiology*; D014801:Vitamin A / Q000493:pharmacokinetics*; D000099214:Retinol-Binding Proteins, Interstitial
chemical_list: D016895:Culture Media, Serum-Free; D005136:Eye Proteins; D012177:Retinol-Binding Proteins; D014801:Vitamin A; D000099214:Retinol-Binding Proteins, Interstitial
keywords: IRBP; Müller cell; photoreceptors; retina; visual cycle