Boyle David, Blair Salvatore D, Chamot Danuta, Goss Greg G
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
Comp Biochem Physiol A Mol Integr Physiol. 2016 Nov;201:30-36. doi: 10.1016/j.cbpa.2016.06.027. Epub 2016 Jun 25.
Developing freshwater fish must compensate for the loss of ions, including sodium (Na(+)), to the environment. In this study, we used a radiotracer flux approach and pharmacological inhibitors to investigate the role of sodium/hydrogen exchange proteins (Nhe) in Na(+) uptake in rainbow trout (Oncorhynchus mykiss) reared from fertilization in soft water (0.1mM Na(+)). For comparison, a second group of embryos/larvae reared in hard water (2.2mM Na(+), higher pH and [Ca(2+)]) were also included in the experiment but were fluxed in soft water, only. Unidirectional rates of Na(+) uptake increased throughout development and were significantly higher in embryos/larvae reared in soft water. However, the mechanisms of Na(+) uptake in both groups of larvae were not significantly different, either in larvae immediately post-hatch or later in development: the broad spectrum Na(+) channel blocker amiloride inhibited 85-90% of uptake and the Nhe-inhibitor EIPA also caused near maximal inhibitions of Na(+) uptake. These data indicated Na(+) uptake was Nhe-mediated in soft water. A role of Nhe3b (but not Nhe2 or Nhe3a) in Na(+) uptake in soft water was also supported through gene expression analyses: expression of nhe3b increased throughout development in whole embryos/larvae in both groups and was significantly higher in those reared in soft water. This pattern of expression correlated well with measurements of Na(+) uptake. Together these data indicate that in part, rainbow trout embryos/larvae reared in low Na(+) soft water maintained Na(+) homeostasis by an EIPA sensitive component of Na(+) uptake, and support a primary role for Nhe3b.
处于发育阶段的淡水鱼必须弥补向环境中流失的离子，包括钠离子（Na⁺）。在本研究中，我们采用放射性示踪剂通量法和药理学抑制剂，研究了钠/氢交换蛋白（Nhe）在软水（0.1mM Na⁺）中受精培育的虹鳟（Oncorhynchus mykiss）摄取Na⁺过程中的作用。为作比较，实验中还纳入了另一组在硬水（2.2mM Na⁺、较高pH值和[Ca²⁺]）中培育的胚胎/幼体，但仅在软水中进行通量测定。Na⁺的单向摄取速率在整个发育过程中均有所增加，且在软水中培育的胚胎/幼体中显著更高。然而，两组幼体摄取Na⁺的机制在孵化后即刻或发育后期均无显著差异：广谱Na⁺通道阻滞剂氨氯吡脒抑制了85 - 90%的摄取，Nhe抑制剂EIPA也几乎完全抑制了Na⁺摄取。这些数据表明，在软水中Na⁺摄取是由Nhe介导的。基因表达分析也支持了Nhe3b（而非Nhe2或Nhe3a）在软水中Na⁺摄取中的作用：两组全胚胎/幼体中nhe3b的表达在整个发育过程中均增加，且在软水中培育的胚胎/幼体中显著更高。这种表达模式与Na⁺摄取的测量结果高度相关。这些数据共同表明，部分在低Na⁺软水中培育的虹鳟胚胎/幼体通过对EIPA敏感的Na⁺摄取成分维持Na⁺稳态，并支持Nhe3b起主要作用。
