Rogers Joseph T, Wood Chris M
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada.
J Exp Biol. 2004 Feb;207(Pt 5):813-25. doi: 10.1242/jeb.00826.
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.
在淡水虹鳟鱼（Oncorhynchus mykiss）中研究了鳃对铅的摄取机制以及与钙（Ca(2+)）转运的相互作用。分别暴露于2.3±0.1和1.4±0.2微摩尔/升溶解铅0至48小时后，铅显著降低了钙的流入，分别降低了约40%和30%。铅对钙流入的急性抑制表现出典型的米氏动力学，米氏常数（K(m)）增加了约16倍，而最大反应速度（J(max)）值没有显著变化，抑制剂常数（K(i,Pb)）为0.48微摩尔/升。其他分析表明，在测试的最高铅浓度（4.8微摩尔/升）下，可能存在混合竞争/非竞争相互作用。随着水体中钙浓度的增加，鳃对铅的积累减少，这表明钙对鳃摄取铅具有保护作用。在暴露水中添加镧（1微摩尔/升）会同时抑制钙和铅的顶端进入（分别为55%和77%）。使用镉（1微摩尔/升）和锌（100微摩尔/升）作为非电压依赖性钙通道竞争者也分别使鳃对铅的摄取减少了约56%和47%。硝苯地平和维拉帕米（高达100微摩尔/升）这两种电压依赖性钙通道阻滞剂对鳃中铅的积累没有影响。注射氯化钙减少了鳃对钙和铅的摄取。这表明铅通过顶端非电压依赖性钙通道转运，类似于钙的进入。高亲和力钙-ATP酶活性没有受到铅的急性影响，但在暴露于5.5±0.4微摩尔/升溶解铅96小时期间，活性显著降低了80%，这表明铅诱导的钙破坏可能存在非竞争成分。研究了铅对钙流出的影响，发现其影响不显著。我们得出结论，铅的摄取至少部分是通过与钙相同的机制发生的，这导致钙流入的破坏并最终导致钙稳态的破坏。
