title: Waterborne iron acquisition by a freshwater teleost fish, zebrafish Danio rerio.
abstract: Waterborne iron accumulation by the gills of the zebrafish Danio rerio was assessed in ion-poor water. Branchial iron uptake, which comprises both the iron that has entered the gill cells and iron that is strongly bound to the epithelia, has high- and low-affinity components. At low nominal [Fe] (<40 nmol l(-1)) the high-affinity component demonstrated saturation kinetics, with an apparent K(m) of 5.9 nmol l(-1) Fe and V(max) of 2.1 pmol g(-1) h(-1). Over a range of higher nominal [Fe] (40-200 nmol l(-1)), branchial uptake was linear. In the presence of 2 micro mol l(-1) of the reducing agent dithiothreitol (DTT), branchial iron accumulation was significantly enhanced at [Fe]>15 nmol l(-1). The proton pump inhibitor bafilomycin A significantly reduced iron uptake in the presence of DTT. On the basis of these observations we conclude that branchial iron uptake at low [Fe] shows characteristics similar to those of other iron-transporting epithelia, coupling an apical membrane ferric reductase to a Fe(2+)/H(+) symporter. Zebrafish branchial iron transport at 18.6 nmol l(-1) was inhibited by 200 nmol l(-1) Cd(2+). But, unlike other Fe(2+)/H(+) symporters, iron uptake was not affected by other divalent metals (Co(2+), Ni(2+), Pb(2+), Cu(2+), Zn(2+) and Mn(2+)). Zebrafish loaded with (59)Fe from the water showed a loss of 7.9 pmol Fe g(-1) body mass over the first day and a further loss of 5.7 pmol Fe g(-1) body mass over the following 28 days. The depuration kinetics followed a two-component exponential model; for the short-lived component, t(1/2)=0.31 days, and for the long-lived component, t(1/2)=13.2 days. The daily iron loss by zebrafish can be compensated by iron uptake at exceedingly low water iron concentrations (uptake rate at 1.625 nmol l(-1) Fe=0.425 pmol g(-1) h(-1)), demonstrating that uptake of iron from the water is potentially an important source of this nutritive metal in freshwater teleost fish.
authors.affiliation: Zoophysiological Laboratory, The August Krogh Institute, University of Copenhagen, Denmark. nic.bury@kcl.ac.uk
authors.forename: Nicolas R
authors.initials: NR
authors.lastname: Bury
authors.forename: Martin
authors.initials: M
authors.lastname: Grosell
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002104:Cadmium / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D005618:Fresh Water; D005880:Gills / Q000378:metabolism*; D007501:Iron / Q000378:metabolism / Q000493:pharmacokinetics*; D018942:Macrolides / Q000494:pharmacology; D008954:Models, Biological; D015027:Zebrafish / Q000378:metabolism*
chemical_list: D018942:Macrolides; D002104:Cadmium; C057620:bafilomycin A; D007501:Iron; D004229:Dithiothreitol