title: Evidence for aerobic ATP synthesis in isolated myelin vesicles.
abstract: Even though brain represents only 2-3% of the body weight, it consumes 20% of total body oxygen, and 25% of total body glucose. This sounds surprising, in that mitochondrial density in brain is low, while mitochondria are thought to be the sole site of aerobic energy supply. These data would suggest that structures other than mitochondria are involved in aerobic ATP production. Considering that a sustained aerobic metabolism needs a great surface extension and that the oxygen solubility is higher in neutral lipids, we have focused our attention on myelin sheath, the multilayered membrane produced by oligodendrocytes, hypothesizing it to be an ATP production site. Myelin has long been supposed to augment the speed of conduction, however, there is growing evidence that it exerts an as yet unexplained neuro-trophic role. In this work, by biochemical assays, Western Blot analysis, confocal laser microscopy, we present evidence that isolated myelin vesicles (IMV) are able to consume O(2) and produce ATP through the operation of a proton gradient across their membranes. Living optic nerve sections were exposed to MitoTracker, a classical mitochondrial dye, by a technique that we have developed and it was found that structures closely resembling nerve axons were stained. By immunohistochemistry we show that ATP synthase and myelin basic protein colocalize on both IMV and optic nerves. The complex of data suggests that myelin sheath may be the site of oxygen absorption and aerobic metabolism for the axons.
authors.affiliation: Biology Department, University of Genova, Faculty of Sciences MFN, Viale Benedetto XV, Genoa, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Ravera
authors.forename: Isabella
authors.initials: I
authors.lastname: Panfoli
authors.forename: Daniela
authors.initials: D
authors.lastname: Calzia
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Aluigi
authors.forename: Paolo
authors.initials: P
authors.lastname: Bianchini
authors.forename: Alberto
authors.initials: A
authors.lastname: Diaspro
authors.forename: Gianluigi
authors.initials: G
authors.lastname: Mancardi
authors.forename: Alessandro
authors.initials: A
authors.lastname: Morelli
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D000263:Adenylate Kinase / Q000378:metabolism; D000332:Aerobiosis; D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D019069:Cell Respiration; D022162:Cytoplasmic Vesicles / Q000378:metabolism* / Q000648:ultrastructure; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000201:enzymology / Q000648:ultrastructure; D004676:Myelin Basic Protein / Q000378:metabolism; D009186:Myelin Sheath / Q000378:metabolism* / Q000648:ultrastructure; D009900:Optic Nerve / Q000378:metabolism / Q000648:ultrastructure; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D016548:Prosencephalon / Q000201:enzymology; D021381:Protein Transport; D006180:Proton-Translocating ATPases / Q000378:metabolism; D011522:Protons; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D004676:Myelin Basic Protein; D011522:Protons; D000255:Adenosine Triphosphate; D000263:Adenylate Kinase; D006180:Proton-Translocating ATPases; D000254:Sodium-Potassium-Exchanging ATPase