title: Examining urea flux across the intestine of the spiny dogfish, Squalus acanthias.
abstract: Recent examination of urea flux in the intestine of the spiny dogfish shark, Squalus acanthias, has shown that feeding significantly enhances urea uptake across the intestine, and this was significantly inhibited following mucosal addition of phloretin. The present study examined potential mechanisms of urea uptake across the dogfish intestine in starved and fed dogfish. Unidirectional flux chambers were used to examine the kinetics of urea uptake, and to determine the influence of sodium, ouabain, competitive urea analogues, and phloretin on urea uptake across the gut of fed dogfish. Intestinal epithelial preparations from starved and fed dogfish were mounted in Ussing chambers to examine the effect of phloretin on bidirectional solute transport across the intestine. In the unidirectional studies, the maximum uptake rate of urea was found to be 35.3±6.9 μmol.cm(-2).h(-1) and Km was found to be 291.8±9.6 mM in fed fish, and there was a mild inhibition of urea uptake following mucosal addition of competitive agonists. Addition of phloretin, Na-free Ringers and ouabain to the mucosal side of intestinal epithelia also led to a significant reduction in urea uptake in fed fish. In the Ussing chamber studies there was a net influx of urea in fed fish and a small insignificant efflux in starved fish. Addition of phloretin blocked urea uptake in fed fish when added to the mucosal side. Furthermore, phloretin had no effect on ion transport across the intestinal epithelia with the exception of the divalent cations, magnesium and calcium.
authors.affiliation: Department of Biological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada; Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC VOR 1B0, Canada. Electronic address: gary.anderson@umanitoba.ca.
authors.forename: W
authors.initials: W
authors.lastname: Gary Anderson
authors.affiliation: Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC VOR 1B0, Canada.
authors.forename: Chris
authors.initials: C
authors.lastname: McCabe
authors.affiliation: Department of Biological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.
authors.forename: Catherine
authors.initials: C
authors.lastname: Brandt
authors.affiliation: Department of Biology, McMaster University, 1280 Main St. West, Hamilton, ON L8S 4K1, Canada; Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada; Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC VOR 1B0, Canada.
authors.forename: Chris M
authors.initials: CM
authors.lastname: Wood
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D004284:Dogfish / Q000378:metabolism*; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D008297:Male; D010693:Phloretin / Q000494:pharmacology; D014508:Urea / Q000378:metabolism*
chemical_list: D014508:Urea; D008274:Magnesium; D010693:Phloretin; D002118:Calcium
keywords: Dogfish; Elasmobranch; Intestine; Transport; Urea