Taylor Lisa N, Wood Chris M, McDonald D Gordon
McMaster University, Department of Biology, 1280 Main Street West, Hamilton, ON, Canada, L8S 4K1.
Environ Toxicol Chem. 2003 Sep;22(9):2159-66. doi: 10.1897/02-256.
The main objective of the study was to use a species comparison approach in order to understand sensitivity and tolerance differences to copper. We hypothesized that species differences in toxicity would be reflected by differences in copper binding to high-affinity sites on the gill. Specifically, the strength of copper binding (affinity, logK) and maximum number of binding sites (saturation, Bmax) for copper at the gill surface would vary among different species of fish. Two species that are different in their copper sensitivity are the rainbow trout (Oncorhynchus mykiss) and yellow perch (Perca flavescens). We explicitly compared acute toxicity (median lethal concentrations via 96-h LC50s) and whole-body Na+ loss in both organisms in two distinct water chemistries (i.e., hard and soft water). For both species, the copper binding sites at the gill surface were characterized for their affinity and saturability. The binding properties of the gill were quite similar between the two species in each water chemistry. Based on estimations of the free cupric ion concentration, the affinity, or logK, was 8.4 for both species in soft water, whereas in hard water, the affinity was higher (approximately 9.7). The Bmax value in soft water was 1.88 nmol/g for rainbow trout and yellow perch, while in hard water, saturation occurred at 3.63 nmol/g for rainbow trout and 9.01 nmol/g for yellow perch. More importantly, the amount of copper bound to the gills at 50% mortality (i.e., lethal accumulation; the LA50) was different between the two species (yellow perch LA50s were nine times higher than those of rainbow trout in soft water and hard water), indicating that the copper binding to the yellow perch gill must not have been 'biologically reactive.' According to 96-h LC50s, yellow perch were less sensitive to copper than were rainbow trout; however, the difference between the two species was similar in hard water (1.05 vs 4.16 microM) and soft water (approximately 0.10 vs 0.44 microM). Perch were more tolerant because they lost less sodium upon exposure to copper; yet this mechanism of tolerance was not reflected by the amount of copper at the gill surface. The influence of water chemistry on the binding properties of the gill demonstrates the dynamic nature of the gill in maintaining ionoregulatory homeostasis, a key issue in the future development of the chronic biotic ligand model.
该研究的主要目的是采用物种比较方法，以了解对铜的敏感性和耐受性差异。我们假设毒性的物种差异将通过铜与鳃上高亲和力位点结合的差异来体现。具体而言，鳃表面铜的结合强度（亲和力，logK）和最大结合位点数（饱和度，Bmax）在不同鱼类物种间会有所不同。在对铜的敏感性方面存在差异的两个物种是虹鳟（Oncorhynchus mykiss）和黄鲈（Perca flavescens）。我们明确比较了这两种生物在两种不同水化学条件（即硬水和软水）下的急性毒性（通过96小时半数致死浓度即LC5０s）和全身钠流失情况。对于这两个物种，都对鳃表面的铜结合位点进行了亲和力和饱和度特征分析。在每种水化学条件下，两个物种鳃的结合特性相当相似。根据游离铜离子浓度的估算，在软水中，两个物种的亲和力即logK均为8.4，而在硬水中，亲和力更高（约为9.7）。在软水中，虹鳟和黄鲈的Bmax值为1.88 nmol/g，而在硬水中，虹鳟的饱和度出现在3.63 nmol/g，黄鲈为9.01 nmol/g。更重要的是，在50%死亡率时（即致死积累量；LA50），两个物种鳃上结合的铜量不同（在软水和硬水中，黄鲈的LA50比虹鳟高九倍），这表明铜与黄鲈鳃的结合一定不是“生物活性的”。根据96小时LC5０s，黄鲈对铜的敏感性低于虹鳟；然而，在硬水（分别为1.05和4.16 microM）和软水（约为0.10和0.44 microM）中，两个物种之间的差异相似。鲈鱼更具耐受性，因为它们在接触铜时钠流失较少；然而，这种耐受机制并未通过鳃表面的铜量体现出来。水化学对鳃结合特性的影响证明了鳃在维持离子调节稳态方面的动态性质，这是慢性生物配体模型未来发展中的一个关键问题。
