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First published online August 8, 2003

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The Journal of Experimental Biology 206, 3285-3292 (2003)
doi: 10.1242/jeb.00554

Regulation of a renal urea transporter with reduced salinity in a marine elasmobranch, Raja erinacea

Robyn L. Morgan, James S. Ballantyne and Patricia A. Wright^*

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 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.

Key words: osmoregulation, trimethylamine oxide, urea transporter gene, skate, Raja erinacea

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