Cutler C P, Phillips C, Hazon N, Cramb G
Department of Biology, Georgia Southern University, Statesboro, GA, USA.
Gen Comp Endocrinol. 2007 Jun-Jul;152(2-3):310-3. doi: 10.1016/j.ygcen.2007.01.031. Epub 2007 Feb 1.
Previous studies in eel (Anguilla anguilla) gill have shown that the expression of the aquaporin 3 (AQP3) water and small solute channel is dramatically decreased (mRNA abundance decreased by up to 97%) when these euryhaline fish are acclimated from freshwater (FW) to seawater (SW). However, AQP3 mRNA expression levels in the intestine following SW-acclimation do not change. The SW-acclimating corticosteroid hormone, cortisol has previously been shown to regulate the expression of aquaporins (particularly AQP1) in eel osmoregulatory tissues in a tissue-specific and isoform-specific fashion. AQP1 is up-regulated in intestine and oesophagus, but down-regulated in kidney, following SW-acclimation in these fish. This study extends knowledge of the regulation of aquaporin expression by cortisol in the eel and shows that elevated levels of this hormone down-regulate AQP3 mRNA expression in the gill in a similar manner to SW-acclimation. However, the smaller magnitude of the changes in branchial AQP3 expression induced by cortisol-infusion (around a 60% decrease), in comparison to those occurring following SW-acclimation, suggest that other factors must also contribute to AQP3 down-regulation. In a similar fashion to the regulation of AQP1 by cortisol, changes in AQP3 expression following hormone infusion appear to be tissue-specific, as little effect was seen on the level of AQP3 expression in the intestine. Again the apparent lack of change in intestinal AQP3 expression following cortisol-infusion mimicked the invariant level of intestinal AQP3 mRNA abundance following SW-acclimation.
先前对欧洲鳗鲡鳃的研究表明，当这些广盐性鱼类从淡水（FW）适应到海水（SW）时，水通道蛋白3（AQP3）水和小分子溶质通道的表达会显著降低（mRNA丰度降低高达97%）。然而，适应海水后肠道中AQP3 mRNA的表达水平没有变化。先前已表明，适应海水的皮质类固醇激素皮质醇以组织特异性和亚型特异性的方式调节鳗鲡渗透调节组织中水通道蛋白（特别是AQP1）的表达。在这些鱼类适应海水后，AQP1在肠道和食管中上调，但在肾脏中下调。本研究扩展了对皮质醇在鳗鲡中水通道蛋白表达调控的认识，并表明这种激素水平的升高以与适应海水类似的方式下调鳃中AQP3 mRNA的表达。然而，与适应海水后相比，皮质醇注入诱导的鳃中AQP3表达变化幅度较小（约60%的下降），这表明其他因素也必定导致AQP3下调。与皮质醇对AQP1的调控方式类似，激素注入后AQP3表达的变化似乎具有组织特异性，因为对肠道中AQP3表达水平几乎没有影响。同样，皮质醇注入后肠道中AQP3表达明显缺乏变化，这与适应海水后肠道中AQP3 mRNA丰度不变的情况相似。
