汞對於斑馬魚仔魚側線感覺與離子調節功能之影響

Abstract

汞（Hg）是一種具高毒性的重金屬，非常容易藉由生物累積的方式進入食物鏈。其毒性取決於他的化學結構、接觸途徑以及物種，目前已有許多在人體及哺乳類動物實驗中，證明長期暴露在汞確實會造成損傷，即使是在低濃度下仍有極高的風險。先前對於汞造成斑馬魚影響的研究相當多，主題大多著重在汞對於斑馬魚胚胎時期神經與腦部發育的影響，較少去探討孵化後仔魚暴露在含汞的環境下，其皮表的離子細胞以及毛細胞的影響。本實驗利用斑馬魚仔魚作為模式物種，分別暴露於短時間（4 hrs）與長時間（48 hrs）含汞（氯化汞、甲基汞）的水體當中，觀察仔魚表皮的毛細胞與離子細胞；這兩型細胞分別負責機械性感受器的功能、排酸功能。短時間暴露於氯化汞和甲基汞後，導致仔魚表皮之毛細胞與離子細胞的細胞數目與功能下降；進而觀察到仔魚逆流行為、活動力以及體內鈣和鈉含量下降。長時間暴露後，於較低的濃度即可觀察到汞所造成的影響，包括細胞數目與功能的下降、逆流行為、體內離子含量及基因表現量的改變。另外，於本實驗我們也觀察到氯化汞與甲基汞所造成的毒性不盡相同。Mercury (Hg) is a highly toxic heavy metal that may accumulate in the food chain through biomagnification and cumulative effects. Previous studies of mercury mostly focused on the effects on the nervous system of zebrafish embryos during their developmental stages, however, the effect on the epidermal cells has not been investigated. The purpose of this study is to investigate the effects of water borne mercury (methylmercury and mercury chloride) on the skin ionocytes and hair cells which are respectively responsible for ionic regulation and mechanical sensory in zebrafish larvae. After short-term（4 hrs）exposures, mercury chloride （HgCl2）and methylmercury ( CH3HgCl ) significantly reduced the number and function of hair cells and ionocytes. The Ca2+ and Na+ contents of the larvae decreased after Hg exposures. The rheotaxis and activity of the larvae decreased after Hg exposures. After long-term (48 hrs) exposures, we observed declines in the numbers of hair cell and ionocyte, whole body ionic contents, and rheotaxis behavior at lower concentrations. We also found that the toxicity was different between methylmercury and mercury chloride.