Characterization of Ni transport into brush border membrane vesicles (BBMVs) isolated from the kidney of the freshwater rainbow trout (Oncorhynchus mykiss).
The transport of nickel (Ni) across the renal brush border membrane of the rainbow trout was examined in vitro using brush border membrane vesicles (BBMVs). Both transmembrane transport of Ni into an osmotically active intravesicular space, and binding of Ni to the brush border membrane itself, were confirmed. Nickel (Ni) uptake fitted a two component kinetic model. Saturable, temperature-dependent transport dominated at lower Ni concentrations, with a moderate linear diffusive component of Ni transport apparent at higher Ni concentrations. An affinity constant (K(m)) for Ni transport within the specifically described vesicular media was calculated as 17.9+/-1.9 microM, the maximal rate of transport (J(max)) was calculated as 108.3+/-3.7 nmol mg protein(-1) min(-1), and the slope of the linear diffusive component was calculated as 0.049+/-0.005 nmol mg protein(-1) min(-1) per microM of Ni. Efflux of Ni from BBMVs was fitted to an exponential decay curve with a half-time (T(1/2)) of 125.2+/-7.3 s. Ni uptake into renal BBMVs was inhibited by magnesium at a 100:1 Mg to Ni molar ratio, and by magnesium and calcium at a 1000:1 molar ratio. In the presence of histidine at a 100:1 histidine to Ni ratio, Ni uptake was almost completely abolished. At a 1:1 molar ratio, histidine inhibited Ni uptake by approximately 50%. Ni-histidine complexation was rapid, with a T(1/2) of 12.2 s describing the Ni-histidine equilibration time needed to inhibit Ni uptake into renal BBMVs by 50%. Characterization of Ni transport across cellular membranes is an important step in understanding both the processes underlying homeostatic regulation of Ni, and the toxicological implications of excessive Ni exposure in aquatic ecosystems.
Pane
Eric F
EF
Department of Biology, McMaster University, 1280 Main St. West, Hamilton, ON, Canada L8S 4K1. epane@mbari.org
Glover
Chris N
CN
Patel
Monika
M
Wood
Chris M
CM
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002412:Cations / Q000737:chemistry; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D011232:Chemical Precipitation; D006639:Histidine / Q000737:chemistry; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism*; D008871:Microvilli / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D009532:Nickel / Q000737:chemistry* / Q000378:metabolism; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D013395:Sucrose / Q000737:chemistry
D000596:Amino Acids; D002412:Cations; D006639:Histidine; D013395:Sucrose; D009532:Nickel