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