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First published online November 13, 2009
Journal of Experimental Biology 212, 3846-3856 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.034157
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The responses of zebrafish (Danio rerio) to high external ammonia and urea transporter inhibition: nitrogen excretion and expression of rhesus glycoproteins and urea transporter proteins

Marvin H. Braun1,*, Shelby L. Steele2 and Steve F. Perry2

1 Hotchkiss Brain Institute, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1
2 University of Ottawa, 30 Marie Curie, Ottawa, ON, Canada K1N 6N5

* Author for correspondence (mhbraun{at}ucalgary.ca)

Accepted 18 August 2009

While adult zebrafish, Danio rerio, possess ammonia and urea transporters (Rh and UT proteins, respectively) in a number of tissues, they are most heavily concentrated within the gills. UT has a diffuse expression pattern within Na+-K+-ATPase (NKA)-type mitochondrion-rich cells and Rh proteins form a network similar to the arrangement seen in pufferfish gills (Nakada et al., 2007b). Rhag expression appeared to be limited to the pillar cells lining the blood spaces of the lamellae while Rhbg was localized to the outer layer of both the lamellae and the filament, upon the pavement cells. Exposure to high external ammonia (HEA) or phloretin increased tissue levels of ammonia and urea, respectively, in adult and juvenile zebrafish; however, the responses to these stressors were age dependent. HEA increased mRNA levels for a number of Rh proteins in embryos and larvae but did not elicit similar effects in adult gills, which appear to compensate for the unfavourable ammonia excretory gradient by increasing expression of V-type H+-ATPase. Phloretin exposure increased UT mRNA levels in embryos and larvae but was without effect in adult gill tissue. Surprisingly, in both adults and juveniles, HEA increased the mRNA expression of UT and phloretin increased the mRNA expression of Rh proteins. These results imply that, in zebrafish, there may be a tighter link between ammonia and urea excretion than is thought to occur in most teleosts.

Key words: Rh glycoproteins, urea transporter, ammonia transport, gills, gene expression


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