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First published online August 8, 2003
Urea transport in kidney brush-border membrane vesicles from an elasmobranch, Raja erinacea
Department of Zoology, University of Guelph, Guelph, Ontario, Canada, N1G 2W1
* Author for correspondence (e-mail: patwrigh{at}uoguelph.ca)
Accepted 23 June 2003
Marine elasmobranch fishes maintain high urea concentrations and therefore must minimize urea loss to the environment in order to reduce the energetic costs of urea production. Previous studies have identified a facilitated urea transporter in the kidney of the dogfish. We examined mechanisms of urea transport in the kidney of the little skate Raja erinacea using an isolated brush-border membrane vesicle preparation. Urea uptake by brush-border membrane vesicles is by a phloretin-sensitive, non-saturable uniporter in the dorsal section and a phloretin-sensitive, sodium-linked urea transporter (Km=0.70 mmol l1, Vmax=1.18 µmol h1 mg1 protein) in the ventral section of the kidney. This provides evidence for two separate urea transporters in the dorsal versus ventral sections of the kidney. We propose that these two mechanisms of urea transport are critical for renal urea reabsorption in the little skate.
Key words: brush-border plasma membrane, phloretin, urea permeability, little skate, Raja erinacea
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