title: The mitochondrial transporter of ascorbic acid functions with high affinity in the presence of low millimolar concentrations of sodium and in the absence of calcium and magnesium.
abstract: We recently reported that U937 cell mitochondria express a functional Na+-dependent ascorbic acid (AA) transporter recognised by anti-SVCT2 antibodies. The present study confirms and extends these observations by showing that this transporter is characterised by a Km and a pH-dependence comparable with that reported for the plasma membrane SVCT2. In isolated mitochondria, Na+ increased AA transport rate in a cooperative manner, revealed by a sigmoid curve and a Hill coefficient of 2, as also observed in intact Raw 264.7 cells (uniquely expressing SVCT2). There was however a striking difference on the Na+ concentrations necessary to reach saturation, i.e., 1 or 100 mM for the mitochondrial and plasma membrane transporters, respectively. Furthermore the mitochondrial, unlike the plasma membrane, transporter was fully active also in the absence of added Ca++ and/or Mg++. Taken together, the results presented in this study indicate that the U937 cell mitochondrial transporter of AA, because of its very low requirement for Na+ and independence for Ca++ and Mg++, displays kinetic characteristics surprisingly similar with those of the plasma membrane SVCT2.
authors: Dipartimento di Scienze Biomolecolari, Università degli Studi di Urbino "Carlo Bo", 61029 Urbino, Italy.
authors: Mara
authors: M
authors: Fiorani
authors: Dipartimento di Scienze Biomolecolari, Università degli Studi di Urbino "Carlo Bo", 61029 Urbino, Italy.
authors: Catia
authors: C
authors: Azzolini
authors: Dipartimento di Scienze Biomolecolari, Università degli Studi di Urbino "Carlo Bo", 61029 Urbino, Italy.
authors: Liana
authors: L
authors: Cerioni
authors: Dipartimento di Scienze Biomolecolari, Università degli Studi di Urbino "Carlo Bo", 61029 Urbino, Italy.
authors: Maddalena
authors: M
authors: Scotti
authors: Dipartimento di Scienze Biomolecolari, Università degli Studi di Urbino "Carlo Bo", 61029 Urbino, Italy.
authors: Andrea
authors: A
authors: Guidarelli
authors: Dipartimento di Scienze della Terra, della Vita e dell'Ambiente, Università degli Studi di Urbino "Carlo Bo", 61029 Urbino, Italy.
authors: Caterina
authors: C
authors: Ciacci
authors: Dipartimento di Scienze Biomolecolari, Università degli Studi di Urbino "Carlo Bo", 61029 Urbino, Italy. Electronic address: orazio.cantoni@uniurb.it.
authors: Orazio
authors: O
authors: Cantoni
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology*; D060347:Sodium-Coupled Vitamin C Transporters / Q000378:metabolism; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D020298:U937 Cells
chemical_list: D033681:Mitochondrial Membrane Transport Proteins; C555163:SLC23A2 protein, human; D060347:Sodium-Coupled Vitamin C Transporters; D012964:Sodium; D008274:Magnesium; D001205:Ascorbic Acid; D002118:Calcium
keywords: Ascorbic acid; Ascorbic acid transport; Mitochondria; Na(+)-dependent ascorbic acid transporter 2