title: Expression and molecular characterization of rat renal D-mannose transport in Xenopus oocytes.
abstract: Renal reabsorption appears to play a major role in d-mannose homeostasis. Here we show that in rat kidney, the transport of d-mannose by brush border membrane vesicles from tubular epithelial cells involves an uphill and rheogenic Na-dependent system, which is fully inhibited by d-mannose itself, incompletely inhibited by d-glucose, d-fructose, phloridzin, and phloretin, and noninhibited by l-mannose or disaccharides. In addition, this system exhibits both low capacity (112.9+/-15.6 pmol/mg/second) and high affinity (0.18+/-0.04 mm), with a 2:1 stoichiometry for the Na:d-mannose interaction, and low affinity for sodium (16.6+/-3.67 mm). We also show expression of d-mannose transport by Xenopus laevis oocytes injected with rat renal polyA(+) RNA. Kinetic analysis of the expressed transport was performed after RNA enrichment by fractionation through a sucrose density gradient and was shown to be identical to that measured in membrane vesicles. The RNA species encoding the expressed transport has a small mean size, 1 kb approximately, and shows no homology with the SGLT family of Na-dependent d-glucose transporters, as shown by low stringent RT-PCR and northern analysis. The expressed transport is specific for d-mannose, since in spite of a significant inhibition by d-glucose and d-fructose, neither of these two substrates was transported above the level of the water-injected oocytes.
authors.affiliation: Department of Toxicology, University of Zaragoza, Miguel Servet 177, E-50.013 Zaragoza, Spain.
authors.forename: T
authors.initials: T
authors.lastname: Blasco
authors.forename: J J
authors.initials: JJ
authors.lastname: Aramayona
authors.forename: A I
authors.initials: AI
authors.lastname: Alcalde
authors.forename: N
authors.initials: N
authors.lastname: Halaihel
authors.forename: M
authors.initials: M
authors.lastname: Sarasa
authors.forename: V
authors.initials: V
authors.lastname: Sorribas
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002458:Cell Fractionation; D005632:Fructose / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D007672:Kidney Cortex / Q000378:metabolism*; D007700:Kinetics; D008358:Mannose / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics; D008871:Microvilli / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000235:genetics; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D010693:Phloretin / Q000494:pharmacology; D010695:Phlorhizin / Q000494:pharmacology; D012333:RNA, Messenger / Q000302:isolation & purification / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D051269:Sodium-Glucose Transporter 1; D013395:Sucrose / Q000737:chemistry; D022161:Transport Vesicles / Q000378:metabolism; D014981:Xenopus / Q000235:genetics / Q000378:metabolism*
chemical_list: D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; D051269:Sodium-Glucose Transporter 1; D005632:Fructose; D013395:Sucrose; D010695:Phlorhizin; D005947:Glucose; D008358:Mannose; D010693:Phloretin