MacIver Bryce, Cutler Christopher P, Yin Jia, Hill Myles G, Zeidel Mark L, Hill Warren G
Nephrology Division, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA.
J Exp Biol. 2009 Sep 1;212(17):2856-63. doi: 10.1242/jeb.025882.
The European eel is a euryhaline teleost which has been shown to differentially up- and downregulate aquaporin (AQP) water channels in response to changes in environmental salinity. We have characterized the transport properties of four aquaporins localized to osmoregulatory organs - gill, esophagus, intestine and kidney. By sequence comparison these four AQP orthologs resemble human AQP1 (eel AQP1), AQP3 (eel AQP3) and AQP10 (AQPe). The fourth member is a duplicate form of AQP1 (AQP1dup) thought to arise from a duplication of the teleost genome. Using heterologous expression in Xenopus oocytes we demonstrate that all four eel orthologs transport water and are mercury inhibitable. Eel AQP3 and AQPe also transport urea and glycerol, making them aquaglyceroporins. Eel AQP3 is dramatically inhibited by extracellular acidity (91% and 69% inhibition of water and glycerol transport respectively at pH 6.5) consistent with channel gating by protons. Maximal water flux of eel AQP3 occurred around pH 8.2 - close to the physiological pH of plasma in the eel. Exposure of AQP-expressing oocytes to heavy metals revealed that eel AQP3 is highly sensitive to extracellular nickel and zinc (88.3% and 86.3% inhibition, respectively) but less sensitive to copper (56.4% inhibition). Surprisingly, copper had a stimulatory effect on eel AQP1 (153.7% activity of control). Copper, nickel and zinc did not affect AQP1dup or AQPe. We establish that all four eel AQP orthologs have similar transport profiles to their human counterparts, with eel AQP3 exhibiting some differences in its sensitivity to metals. This is the first investigation of the transport properties and inhibitor sensitivity of salinity-regulated aquaporins from a euryhaline species. Our results indicate a need to further investigate the deleterious effects of metal pollutants on AQP-containing epithelial cells of the gill and gastrointestinal tract at environmentally appropriate concentrations.
欧洲鳗鲡是一种广盐性硬骨鱼，已证明其会根据环境盐度的变化，差异性地上调或下调水通道蛋白（AQP）水通道。我们已对定位于渗透调节器官（鳃、食道、肠道和肾脏）的四种水通道蛋白的转运特性进行了表征。通过序列比较，这四种AQP直系同源物类似于人类的AQP1（鳗鲡AQP1）、AQP3（鳗鲡AQP3）和AQP10（AQPe）。第四个成员是AQP1的重复形式（AQP1dup），被认为是由硬骨鱼基因组的重复产生的。利用非洲爪蟾卵母细胞中的异源表达，我们证明所有四种鳗鲡直系同源物都能转运水且对汞敏感。鳗鲡AQP3和AQPe也能转运尿素和甘油，使其成为水甘油通道蛋白。鳗鲡AQP3受到细胞外酸度的显著抑制（在pH 6.5时，水和甘油转运分别受到91%和69%的抑制），这与质子对通道的门控作用一致。鳗鲡AQP3的最大水通量出现在pH 8.2左右——接近鳗鲡血浆的生理pH值。将表达AQP的卵母细胞暴露于重金属中发现，鳗鲡AQP3对细胞外镍和锌高度敏感（分别抑制88.3%和86.3%），但对铜不太敏感（抑制56.4%）。令人惊讶的是，铜对鳗鲡AQP1有刺激作用（活性为对照的153.7%）。铜、镍和锌对AQP1dup或AQPe没有影响。我们确定所有四种鳗鲡AQP直系同源物与其人类对应物具有相似的转运特征，鳗鲡AQP3在对金属的敏感性方面表现出一些差异。这是对广盐性物种中盐度调节的水通道蛋白的转运特性和抑制剂敏感性的首次研究。我们的结果表明，有必要进一步研究环境适宜浓度下金属污染物对鳃和胃肠道中含AQP的上皮细胞的有害影响。
