锌对海湾扇贝中镉累积和亚细胞分布的影响

采用室内模拟混合暴露方式,研究了在镉(Cd)质量浓度一定(0.05 mg/L)的条件下,添加不同质量浓度(0 mg/L、0.1 mg/L、0.5 mg/L、1 mg/L)的锌(Zn)对海湾扇贝整体、组织及亚细胞水平Cd累积和分布的影响。结果表明,Zn能显著抑制扇贝全贝对Cd的富集,并且这种抑制作用随暴露时间的延长和Zn浓度的升高而增强。在扇贝不同组织中Zn对Cd的富集均具有抑制作用,其中以鳃最为明显。在亚细胞水平,扇贝各组织累积的Cd主要分布在类金属硫蛋白(MTLP)和细胞碎片(CD)组分。在内脏各亚细胞组分中,Zn对Cd的抑制作用显著,且Zn的加入使CD中的Cd百分比从32%下降到21%~27%,而MTLP中的Cd百分比从57%增加到59%~67%。鳃组织中Zn对Cd百分比的影响更加明显,CD中Cd百分比从36%下降到14%~17%,MTLP中Cd百分比从59%增加到76%~79%;而性腺中MTLP和细胞器(ORG)组分中Cd百分比受Zn浓度影响较为明显,随着Zn浓度的升高,MTLP中Cd百分比下降,而ORG中Cd百分比升高;肌肉组织中Cd含量及百分比分布在亚细胞水平没有明显规律。

Effects of zinc on the accumulation and subcellular distribution of cadmium in the bay scallop, Argopecten irradias

Cadmium is among the most toxic metals in the aquatic environment.Cadmium has unknown biological role and exhibits high toxicity if allowed to accumulate in metabolically-active sites.Many bivalves accumulate high concentrations of cadmium in tissues and organs,particularly scallops,which have a high tolerance to cadmium and accumulate large quantities from the water.Zinc and cadmium often coexist in the aquatic environment and often demonstrate the substitution effect because of their similar chemical properties.Most previous studies have focused on absorption,accumulation,transport,distribution,and detoxification mechanisms in scallops under a single cadmium exposure,but results from mixed-exposure experiments are relatively rare,particularly the effects of zinc exposure on the accumulation and distribution of cadmium in scallop tissues.Because of the potential interaction between essential and non-essential metals,the present study was conducted to investigate the effects of accumulation and distribution of cadmium in bay scallops during short-term exposure to cadmium and zinc.The accumulation and distribution characteristics of cadmium at the whole body,tissue,and subcellular levels of bay scallops,Argopecten irradias,exposed to mixed metals of Zn and Cd were investigated under laboratory conditions.The results showed that exposure to different zinc concentrations inhibited bioaccumulation and distribution of cadmium in bay scallops and was time-and concentration-dependent.Bay scallops concentrated cadmium in all soft tissues,and cadmium content increased over the 7-day exposure.The inhibitory effect of zinc was enhanced as zinc concentration was increased.Cadmium concentrations in different tissues after exposure to the two metals were in the order of:viscera ＞ gill ＞ gonad ＞ muscle,and inhibtory effect by zinc occurred in all tissues,particularly in the gill.Subcellular metal partitioning in bivalves has received increasing attention as it provides valuable information on metal toxicity and bioavailability.Here,subcellular cadmium content was examined following differential centrifugation,which divided the tissues into five subcellular fractions,including metallothionein-like proteins (MTLP),cellular debris (CD),metal-rich granules (MRG),organelles (ORG),and heat-sensitive proteins (HSP).The MTLP fraction was the predominant cadmium-binding compartment,suggesting that MTLP plays a key role detoxifying metals in bay scallops.The CD fraction contained the second largest cadmium fraction,whereas the CD fraction mainly contained tissue fragments and cell membranes.We speculate that the inhibitory effect by zinc on cadmium demonstrates competition between Zn2+ and Cd2+ to bind cell membrane sites.MRG and HSP only played a minor role in cadmium binding.Cadmium content in the metal-sensitive HSP fraction was lower than that in the other subcellular fractions,which may be the reason why scallops have high tolerance to cadmium.Inhibition occurred in all subcellular fractions of the viscera,and the proportion of cadmium in the CD fraction decreased,whereas that in the MTLP fraction increased as zinc was added.Zinc had an antagonistic and protective action on the uptake and toxic effects of cadmium,probably because zinc induces synthesis of MT,which detoxifies cadmium by binding.A similar effect was observed in the gill.However,the percentages of cadmium in the MTLP and ORG fractions of the gonad were affected by zinc concentration.The proportion of cadmium in the MTLP fraction decreased as zinc concentration was increased,whereas the proportion of cadmium in the ORG fraction increased.Cadmium content in the subcellular muscle distribution was relatively low.These results provide insight into the toxic effects of cadmium on bay scallops under mixed-metal exposure,but the mechanisms require further study.