title: Regulation of a renal urea transporter with reduced salinity in a marine elasmobranch, Raja erinacea.
abstract: Marine elasmobranchs retain urea and other osmolytes, e.g. trimethylamine oxide (TMAO), to counterbalance the osmotic pressure of seawater. We investigated whether a renal urea transporter(s) would be regulated in response to dilution of the external environment. A 779 bp cDNA for a putative skate kidney urea transporter (SkUT) was cloned, sequenced and found to display relatively high identity with facilitated urea transporters from other vertebrates. Northern analysis using SkUT as a probe revealed three signals in the kidney at 3.1, 2.8 and 1.6 kb. Upon exposure to 50% seawater, the levels of all three SkUT transcripts were significantly diminished in the kidney (by 1.8- to 3.5-fold). In response to environmental dilution, renal tissue osmolality and urea concentration decreased, whereas water content increased. There were no significant differences in osmolyte and mRNA levels between the dorsal-lateral bundle and ventral sections of the kidney. Taken together, these findings provide evidence that the downregulation of SkUT may play a key role in lowering tissue urea levels in response to external osmolality.
authors.affiliation: Department of Zoology, University of Guelph, Guelph, Ontario, Canada, N1G 2W1.
authors.forename: Robyn L
authors.initials: RL
authors.lastname: Morgan
authors.forename: James S
authors.initials: JS
authors.lastname: Ballantyne
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Wright
mesh_terms: D000595:Amino Acid Sequence; D000704:Analysis of Variance; D000818:Animals; D015152:Blotting, Northern; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D015536:Down-Regulation / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008744:Methylamines / Q000378:metabolism*; D008969:Molecular Sequence Data; D009509:New Brunswick; D009994:Osmolar Concentration; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012623:Seawater; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D012860:Skates, Fish / Q000235:genetics / Q000502:physiology*; D014508:Urea / Q000378:metabolism*; D000096982:Urea Transporters
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D026901:Membrane Transport Proteins; D008744:Methylamines; D014508:Urea; D000096982:Urea Transporters; C005855:trimethyloxamine