title: New findings in ATP supply in rod outer segments: insights for retinopathies.
abstract: BACKGROUND
  The rod outer segment (OS) is the specialised organelle where phototransduction takes place. Our previous proteomic and biochemical analyses on purified rod disks showed the functional expression of the respiratory chain complexes I-IV and F1 Fo -ATP synthase in OS disks, as well as active soluble tricarboxylic acid cycle enzymes. Here, we focussed our study on the whole OS that contains the cytosol and plasma membrane and disks as native flattened saccules, unlike spherical osmotically intact disks.
  
  
  RESULTS
  OS were purified from bovine retinas and characterised for purity. Oximetry, ATP synthesis and cytochrome c oxidase (COX) assays were performed. The presence of COX and F₁F₀-ATP synthase (ATP synthase) was assessed by semi-quantitative Western blotting, immunofluorescence or confocal laser scanning microscopy on whole bovine retinas and bovine retinal sections and by immunogold transmission electron microscopy (TEM) of purified OS or bovine retinal sections. Both ATP synthase and COX are catalytically active in OS. These are able to consume oxygen (O₂) in the presence of pyruvate and malate. CLSM analyses showed that rhodopsin autofluorescence and MitoTracker Deep Red 633 fluorescence co-localise on rod OS. Data are confirmed by co-localisation studies of ATP synthase with Rh in rod OS by immunofluorescence and TEM in bovine retinal sections.
  
  
  CONCLUSIONS
  Our data confirm the expression and activity of COX and ATP synthase in OS, suggestive of the presence of an extra-mitochondrial oxidative phosphorylation in rod OS, meant to supply ATP for the visual transduction. In this respect, the membrane rich OS environment would be meant to absorb both light and O₂. The ability of OS to manipulate O₂ may shed light on the pathogenesis of many retinal degenerative diseases ascribed to oxidative stress, as well as on the efficacy of the treatment with dietary supplements, presently utilised as supporting therapies.
authors: Department of Pharmacy-DIFAR, Biochemistry and Physiology Lab, University of Genoa, Genova, Italy.
authors: Daniela
authors: D
authors: Calzia
authors: Stefano
authors: S
authors: Barabino
authors: Paolo
authors: P
authors: Bianchini
authors: Greta
authors: G
authors: Garbarino
authors: Michele
authors: M
authors: Oneto
authors: Federico
authors: F
authors: Caicci
authors: Alberto
authors: A
authors: Diaspro
authors: Carlo
authors: C
authors: Tacchetti
authors: Lucia
authors: L
authors: Manni
authors: Simona
authors: S
authors: Candiani
authors: Silvia
authors: S
authors: Ravera
authors: Alessandro
authors: A
authors: Morelli
authors: Carlo
authors: C
authors: Enrico Traverso
authors: Isabella
authors: I
authors: Panfoli
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism; D025261:Mitochondrial Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010766:Phosphorylation; D012160:Retina / Q000378:metabolism; D012164:Retinal Diseases / Q000201:enzymology / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000201:enzymology / Q000378:metabolism*
chemical_list: D000255:Adenosine Triphosphate; D003576:Electron Transport Complex IV; C474451:F1F0-ATP synthase; D025261:Mitochondrial Proton-Translocating ATPases; D010100:Oxygen
keywords: Cytochrome c oxydase; F1Fo-ATP synthase; Phototransduction; Respiratory chain complexes; Rod outer segments