Bonneris Emmanuelle, Giguère Anik, Perceval Olivier, Buronfosse Thierry, Masson Stéphane, Hare Landis, Campbell Peter G C
Institut National de la Recherche Scientifique (INRS)--Eau, Terre et Environnement, Université du Québec, 490 de la Couronne, Quebec City, Que., Canada G1K 9A9.
Aquat Toxicol. 2005 Mar 4;71(4):319-34. doi: 10.1016/j.aquatox.2004.11.025. Epub 2005 Jan 22.
Indigenous unionid molluscs, Pyganodon grandis, were collected from nine lakes in the Rouyn-Noranda area (Quebec, Canada) along a polymetallic concentration gradient (Cd, Cu, Zn). After excision, the gills were gently homogenised and the cellular compartments were separated by a differential centrifugation procedure that yielded the following particulate fractions: "nuclei + cellular debris", "mitochondria", "lysosomes + microsomes" and "granules". The supernatant remaining after the final ultracentrifugation step, i.e., the operationally-defined cytosol, was separated into a "heat-denaturable proteins" (HDP) fraction and a "heat-stable proteins" (HSP) fraction containing metallothionein (MT). The Cd, Cu and Zn content of each particulate and cytosolic fraction was determined and gill metallothionein was quantified independently by a mercury saturation assay. Cytosolic Cd concentrations were significantly related to the dissolved Cd concentrations at each site, but cytosolic Cu and Zn (essential metals) were not related to their respective ambient dissolved metal concentrations. Metallothionein concentrations increased along the metal contamination gradient and were related to cytosolic Cd (and Zn) in a concentration-dependent manner. However mass balance calculations showed that binding to metallothionein could only account for a small proportion of total gill metal ( approximately 10% Cd; approximately 3% Cu; approximately 1% Zn). Under these chronic exposure conditions, the three metals (Cd, Cu and Zn) were mainly located in calcium concretions present in the gills (respectively 58 +/- 13% of the total gill Cd, 64 +/- 6% of the total gill Cu and 73 +/- 6% of the total gill Zn). The overall contribution of granules to the total gill dry weight remained relatively constant among the different lakes, suggesting that lake-to-lake variations in granule synthesis were independent of the metal contamination gradient, i.e., these constituent elements of unionid gills act as non-inducible metal sinks at the cellular level. Metal concentrations increased proportionally in both the granules and the MT pool along the polymetallic gradient, suggesting a constant partitioning between these two compartments. Overall, despite an increase in Cd in the "mitochondria" fraction, metal sequestration mechanisms seem to be reasonably effective in detoxifying cadmium: in the cytosol, Cd concentrations in the potentially metal-sensitive HDP fraction remained relatively low and constant, even in specimens collected from the most contaminated lakes.
从加拿大魁北克鲁安 - 诺兰达地区的九个湖泊中，沿着多金属浓度梯度（镉、铜、锌）采集了本地珠蚌属软体动物——巨锉蛤。切除鳃后，将其轻轻匀浆，通过差速离心程序分离细胞区室，得到以下颗粒组分：“细胞核 + 细胞碎片”、“线粒体”、“溶酶体 + 微粒体”和“颗粒”。在最后一次超速离心步骤后剩余的上清液，即操作定义的胞质溶胶，被分离成“热变性蛋白”（HDP）组分和含有金属硫蛋白（MT）的“热稳定蛋白”（HSP）组分。测定每个颗粒和胞质组分中的镉、铜和锌含量，并通过汞饱和法独立定量鳃中的金属硫蛋白。每个位点的胞质镉浓度与溶解镉浓度显著相关，但胞质铜和锌（必需金属）与各自的环境溶解金属浓度无关。金属硫蛋白浓度沿着金属污染梯度增加，并以浓度依赖的方式与胞质镉（和锌）相关。然而，质量平衡计算表明，与金属硫蛋白的结合仅占鳃总金属的一小部分（约10%的镉；约3%的铜；约1%的锌）。在这些慢性暴露条件下，三种金属（镉、铜和锌）主要位于鳃中存在的钙结核中（分别占鳃总镉的58±13%、鳃总铜的64±6%和鳃总锌的73±6%）。颗粒对鳃总干重的总体贡献在不同湖泊之间保持相对恒定，这表明颗粒合成的湖间差异与金属污染梯度无关，即这些珠蚌鳃的组成元素在细胞水平上作为不可诱导的金属库。沿着多金属梯度，颗粒和MT库中的金属浓度成比例增加，表明这两个区室之间存在恒定的分配。总体而言，尽管“线粒体”组分中的镉增加，但金属螯合机制似乎在有效解毒镉方面相当有效：在胞质溶胶中，即使在从污染最严重的湖泊采集的样本中，潜在对金属敏感的HDP组分中的镉浓度仍保持相对较低且恒定。
