title: Mechanism of branchial apical silver uptake by rainbow trout is via the proton-coupled Na(+) channel.
abstract: The branchial uptake mechanism of the nonessential heavy metal silver from very dilute media by the gills of freshwater rainbow trout was investigated. At concentrations >36 nM AgNO(3), silver rapidly entered the gills, reaching a peak at 1 h, after which time there was a steady decline in gill silver concentration and a resulting increase in body silver accumulation. Below 36 nM AgNO(3), there was only a very gradual increase in gill and body silver concentration over the 48-h exposure period. Increasing water sodium concentration ([Na(+)]; 0.05 to 21 mM) significantly reduced silver uptake, although, in contrast, increasing ambient [Ca(2+)] or [K(+)] up to 10 mM did not reduce silver uptake. Kinetic analysis of silver uptake at varying [Na(+)] showed a significant decrease in maximal silver transport capacity (173 +/- 34 pmol. g(-1). h(-1) at 0.1 mM [Na(+)] compared with 35 +/- 9 at 13 mM [Na(+)]) and only a slight decrease in the affinity for silver transport (K(m); 55 +/- 27 nM at 0.1 mM [Na(+)] compared with 91 +/- 47 nM at 13 mM [Na(+)]). Phenamil (a specific blocker of Na(+) channels), at a concentration of 100 microM, blocked Na(+) uptake by 78% of control values (58% after washout), and bafilomycin A(1) (a specific blocker of V-type ATPase), at a concentration of 2 microM, inhibited Na(+) uptake by 57% of control values, demonstrating the presence of a proton-coupled Na(+) channel in the apical membrane of the gills. Phenamil (after washout) and bafilomycin A(1) also blocked silver uptake by 62 and 79% of control values, respectively, indicating that Ag(+) is able to enter the apical membrane via the proton-coupled Na(+) channel.
authors.affiliation: Department of Biological Sciences, Hatherly Laboratories, University of Exeter, Exeter, United Kingdom EX4 4PS. n.r.bury@exeter.ac.uk
authors.forename: N R
authors.initials: NR
authors.lastname: Bury
authors.forename: C M
authors.initials: CM
authors.lastname: Wood
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001667:Binding, Competitive; D001692:Biological Transport / Q000502:physiology; D002412:Cations / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005880:Gills / Q000378:metabolism*; D007700:Kinetics; D018942:Macrolides; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D011522:Protons; D012835:Silver Nitrate / Q000493:pharmacokinetics*; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D002412:Cations; D004791:Enzyme Inhibitors; D018942:Macrolides; D011522:Protons; D026941:Sodium Channel Blockers; D015222:Sodium Channels; C047088:phenylamil; D000584:Amiloride; C040929:bafilomycin A1; D012835:Silver Nitrate