Leonard Erin M, Pierce Laura M, Gillis Patricia L, Wood Chris M, O'Donnell Michael J
Department of Biology, McMaster University, Hamilton, ON, Canada.
Aquat Toxicol. 2009 May 5;92(3):179-86. doi: 10.1016/j.aquatox.2009.01.011. Epub 2009 Feb 6.
Many aquatic insects are very insensitive to cadmium in short-term laboratory studies. LC50 values for larvae of the midge Chironomus riparius are over 25,000 times the Criterion Maximum Concentration in the United States Environmental Protection Agency (U.S. EPA (2000)) species sensitivity distribution (SSD). Excretion or sequestration of cadmium may contribute to insensitivity and we have therefore examined cadmium transport by isolated guts and renal tissues of C. riparius larvae. Regional differences of Cd transport along the gut were identified using a Cd(2+)-selective microelectrode in conjunction with the Scanning Ion-Selective Electrode Technique (SIET). Cd is transported into the anterior midgut (AMG) cells from the lumen and out of the cells into the hemolymph. The transport of Cd from the gut lumen to the hemolymph exposes other tissues such as the nervous system and muscles to Cd. The gut segments which remove Cd from the hemolymph at the highest rate are the posterior midgut (PMG) and the ileum. In addition, assays using an isolated Malpighian (renal) tubule preparation have shown that the Malpighian tubules (MT) both sequester and secrete Cd. For larvae bathed in 10 micromol l(-1) Cd, the tubules can secrete the entire hemolymph burden of Cd in approximately 15 h.
在短期实验室研究中，许多水生昆虫对镉非常不敏感。摇蚊（Chironomus riparius）幼虫的半数致死浓度（LC50）值超过了美国环境保护局（U.S. EPA (2000)）物种敏感度分布（SSD）中的标准最大浓度的25000倍。镉的排泄或隔离可能导致这种不敏感性，因此我们研究了摇蚊幼虫分离的肠道和肾组织对镉的转运。使用镉（2+）选择性微电极结合扫描离子选择性电极技术（SIET），确定了沿肠道镉转运的区域差异。镉从肠腔转运到中肠前段（AMG）细胞内，然后从细胞内转运到血淋巴中。镉从肠腔到血淋巴的转运使其他组织如神经系统和肌肉暴露于镉。从血淋巴中去除镉速率最高的肠道部分是中肠后段（PMG）和回肠。此外，使用分离的马氏（肾）小管制剂的试验表明，马氏小管（MT）既能隔离又能分泌镉。对于浸泡在10微摩尔/升镉溶液中的幼虫，小管大约在15小时内可以分泌出血淋巴中全部的镉负荷。
