title: Mechanisms behind Pb-induced disruption of Na+ and Cl- balance in rainbow trout (Oncorhynchus mykiss).
abstract: The mechanism of Pb-induced disruption of Na(+) and Cl(-) balance was investigated in the freshwater rainbow trout (Oncorhynchus mykiss). Na(+) and Cl(-) influx rates were reduced immediately in the presence of 2.40 +/- 0.24 and 1.25 +/- 0.14 muM Pb, with a small increase in efflux rates occurring after 24-h exposure. Waterborne Pb caused a significant decrease in the maximal rate of Na(+) influx without a change in transporter affinity, suggesting a noncompetitive disruption of Na(+) uptake by Pb. Phenamil and bafilomycin markedly reduced Na(+) influx rate but did not affect Pb accumulation at the gill. Time-course analysis in rainbow trout exposed to 0, 0.48, 2.4, and 4.8 microM Pb revealed time- and concentration-dependent branchial Pb accumulation. Na(+)-K(+)-ATPase activity was significantly reduced, with 4.8 microM exposure resulting in immediate enzyme inhibition and 0.48 and 2.4 microM exposures inhibiting activity by 24 h. Reduced activity was weakly correlated with gill Pb accumulation after 3- and 8-h exposures; this relationship strengthened by 24 h. Reduced Na(+) uptake was correlated with gill Pb burden after exposures of 3, 8, and 24 h. Immediate inhibition of branchial carbonic anhydrase activity occurred after 3-h exposure to 0.82 +/- 0.05 or 4.30 +/- 0.05 microM Pb and continued for up to 24 h. We conclude that Pb-induced disruption of Na(+) and Cl(-) homeostasis is in part a result of rapid inhibition of carbonic anhydrase activity and of binding of Pb with Na(+)-K(+)-ATPase, causing noncompetitive inhibition of Na(+) and Cl(-) influx.
authors: Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada. joerogers78@hotmail.com
authors: Joseph T
authors: JT
authors: Rogers
authors: Monika
authors: M
authors: Patel
authors: Kathleen M
authors: KM
authors: Gilmour
authors: Chris M
authors: CM
authors: Wood
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002256:Carbonic Anhydrases / Q000187:drug effects / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005880:Gills / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D007854:Lead / Q000494:pharmacology*; D018942:Macrolides / Q000494:pharmacology; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors; D012964:Sodium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013997:Time Factors; D014882:Water-Electrolyte Balance / Q000187:drug effects*
chemical_list: D002712:Chlorides; D004791:Enzyme Inhibitors; D018942:Macrolides; D026941:Sodium Channel Blockers; C047088:phenylamil; D007854:Lead; D000584:Amiloride; C040929:bafilomycin A1; D012964:Sodium; D006180:Proton-Translocating ATPases; D002256:Carbonic Anhydrases; D000254:Sodium-Potassium-Exchanging ATPase