title: Characterization of branchial lead-calcium interaction in the freshwater rainbow trout Oncorhynchus mykiss.
abstract: The mechanism of branchial lead uptake and interplay with Ca(2+) transport was investigated in the freshwater rainbow trout Oncorhynchus mykiss. Lead significantly reduced Ca(2+) influx by approximately 40% and 30% after exposure to 2.3+/-0.1 and 1.4+/-0.2 micromol l(-1) dissolved lead, respectively, for 0-48 h. Acute inhibition of Ca(2+) influx by lead exhibited typical Michaelis-Menten kinetics with an approximate 16-fold increase in K(m), whereas J(max) values did not significantly change, yielding an inhibitor constant (K(i,Pb)) of 0.48 micromol l(-1). Alternative analyses suggest the possibility of a mixed competitive/non-competitive interaction at the highest lead concentration tested (4.8 micromol l(-1)). Branchial lead accumulation was reduced with increasing waterborne Ca(2+) concentrations, suggesting a protective effect of Ca(2+) against lead uptake at the gill. The apical entries of Ca(2+) and lead were both inhibited (55% and 77%, respectively) by the addition of lanthanum (1 micromol l(-1)) to the exposure water. The use of cadmium (1 micromol l(-1)) and zinc (100 micromol l(-1)) as voltage-independent calcium channel competitors also reduced branchial lead uptake by approximately 56% and 47%, respectively. Nifedipine and verapamil (up to 100 micromol l(-1)), both voltage-dependent calcium channel blockers, had no effect on gill lead accumulation. CaCl(2) injection reduced both Ca(2+) and lead uptake by the gills. This suggests transport of lead through apical voltage-independent calcium channels, similar to the entry of Ca(2+). High-affinity Ca(2+)-ATPase activity was not acutely affected by lead, but a significant 80% reduction in activity occurred during exposure for 96 h to 5.5+/-0.4 micromol l(-1) dissolved lead, indicating a possible non-competitive component to lead-induced Ca(2+) disruption. The effect of lead on Ca(2+) efflux was investigated and found to be insignificant. We conclude that uptake of lead occurs, at least in part, by the same mechanism as Ca(2+), which results in disruption of Ca(2+) influx and ultimately Ca(2+) homeostasis.
authors.affiliation: Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada. joerog@mcmaster.ca
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Rogers
authors.forename: Chris M
authors.initials: CM
authors.lastname: Wood
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002122:Calcium Chloride / Q000494:pharmacology; D005618:Fresh Water; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D007854:Lead / Q000493:pharmacokinetics* / Q000494:pharmacology*; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D009864:Ontario; D015032:Zinc / Q000494:pharmacology
chemical_list: D002104:Cadmium; D007854:Lead; D007811:Lanthanum; D015032:Zinc; D002122:Calcium Chloride; D002118:Calcium