ISSN:
1432-1424
Keywords:
Key words: Mannose transport — Renal reabsorption — Oocyte expression —Xenopus laevis— Membrane vesicles — Rat
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002320010020
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