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Journal of Experimental Biology, Vol 203, Issue 20 3199-3207, Copyright © 2000 by Company of Biologists

JOURNAL ARTICLES

The mechanisms of urea transport by early life stages of rainbow trout (Oncorhynchus mykiss)

CM Pilley and PA Wright
Department of Zoology, University of Guelph, Guelph, Ontario, Canada N1G 2W1. patwrigh@uoguelph.ca

We tested the hypothesis that urea transport in rainbow trout (Oncorhynchus mykiss) embryos is dependent, in part, on a bidirectional urea-transport protein. Acute exposure to phloretin and urea analogs [acetamide, thiourea, 1,(4-nitrophenyl)-2-thiourea] reversibly inhibited urea excretion from the embryos to the external water. Unidirectional urea influx was inhibited by acetamide and thiourea, with IC(50) values of 0.04 and 0.05 mmol l(-1), respectively. Influx of urea from the external water to the embryo tended to saturate at elevated external urea concentrations (V(max)=10.50 nmol g(-1) h(-1); K(m)=2 mmol l(-1)). At very high urea concentrations (20 mmol l(-1)), however, a second, non-saturable component was apparent. These results indicate that urea excretion in trout embryos is dependent, in part, on a phloretin-sensitive facilitated urea transporter similar to that reported in mammalian inner medullary collecting ducts and elasmobranch kidney.
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