title: The mechanisms of urea transport by early life stages of rainbow trout (Oncorhynchus mykiss).
abstract: 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.
authors.affiliation: Department of Zoology, University of Guelph, Guelph, Ontario, Canada N1G 2W1. patwrigh@uoguelph.ca
authors.forename: C M
authors.initials: CM
authors.lastname: Pilley
authors.forename: P A
authors.initials: PA
authors.lastname: Wright
mesh_terms: D000081:Acetamides / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D017686:Oncorhynchus mykiss / Q000196:embryology* / Q000378:metabolism*; D010693:Phloretin / Q000494:pharmacology; D013890:Thiourea / Q000494:pharmacology; D014508:Urea / Q000031:analogs & derivatives / Q000378:metabolism*
chemical_list: D000081:Acetamides; D014508:Urea; C030686:acetamide; D013890:Thiourea; D010693:Phloretin