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TP3 Metals in the Environment: Dietary Concerns in Aquatic Systems
() Dietary uptake of copper in the rainbow trout: an analysis of mechanisms.
Nadella, Sunita1, Kjoss, Victoria1, Grosell, Martin2, Wood, Chris1, 2, 1 McMaster University, Hamilton, Ontario, Canada2 University of Miami, Miami, Florida, USA
ABSTRACT- Fish require Cu as a micronutrient and can obtain this metal from either water or their diet. Both Na+ - sensitive and Na+ - insensitive mechanisms of branchial Cu uptake have been characterized, however the uptake of dietborne Cu in fish is not well understood. Our research analysed the mechanistic nature of Cu uptake across the intestine of rainbow trout, using radiolabelled Cu (64Cu) and an in vitro gut sac technique. At a mucosal concentration of Cu (50 mol. l -1) approximating the control Cu level in the diet, uptake was linear with time up to 4h in all sections of the intestine. Uptake per unit surface area was twice as great in the anterior intestine relative to the mid and posterior sections. For most treatments however, responses of all gut sections were similar. Experimental manipulation of mucosal NaCl levels (3 − 280 m mol. l -1) resulted in a 2−3 fold increase in Cu uptake. NaSO4 had an identical effect, implicating Na+ rather than the anion. Reversing fluid transport had no effect on Cu transport, eliminating solvent drag as the explanation, and increasing the osmotic pressure with mannitol to mimic the highest Na concentration also had no effect. Increasing Na levels in the mucosal saline resulted in a less negative or more positive serosal side TEP, indicating that Na+ stimulation of Cu transport was not caused by the TEP change. Pretreatment with phenamil, an irreversible blocker of Na transport reduced both Na and Cu uptake by about 35%. The presence of 500 mol. l -1 AgNO3 resulted in a 2-3 fold stimulation of both Na and Cu uptake, an effect which was again independent from changes in TEP. Competition with 500 mol.l -1 ZnSO4 or 500 mol. l -1 Fe(NO3)2 decreased Cu uptake by about 80% while having no effect on the uptake of Na. The study indicates a substantial part of intestinal Cu uptake is Na + − sensitive but by a different mechanism than in the gills. The possibility of DMT1 mediated Cu uptake is also indicated. These results will be interpreted in light of ongoing studies on gastrointestinal Cu uptake in intact trout. (Supported by ICA Human Health & NSERC Strategic Program).
Key words: rainbow trout, dietary metals, Cu, gastrointestinal uptake
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