Brix Kevin V, Grosell Martin
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4K1; The Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA.
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4K1.
Conserv Physiol. 2013 Apr 10;1(1):cot005. doi: 10.1093/conphys/cot005. eCollection 2013.
This study provided an initial characterization of Na(+) uptake in saline freshwater by the endangered pupfish, Cyprinodon macularius. This species occurs only in several saline water systems in the southwestern USA and northern Mexico, where salinity is largely controlled by water-management practices. Consequently, understanding the osmoregulatory capacity of this species is important for their conservation. The lower acclimation limit of C. macularius in freshwater was found to be 2 mM Na(+). Fish acclimated to 2 or 7 mM Na(+) displayed similar Na(+) uptake kinetics, with K m values of 4321 and 3672 μM and V max values of 4771 and 3602 nmol g(-1) h(-1), respectively. A series of experiments using pharmacological inhibitors indicated that Na(+) uptake in C. macularius was not sensitive to bumetanide, metolazone, or phenamil. These results indicate the Na(+)-K(+)-2Cl(-) cotransporter, Na(+)-Cl(-) cotransporter, and the Na(+) channel-H(+)-ATPase system are likely not to be involved in Na(+) uptake at the apical membrane of fish gill ionocytes in fish acclimated to 2 or 7 mM Na(+). However, Na(+) uptake was sensitive to 1 × 10(-3) M amiloride (not 1 × 10(-4) or 1 × 10(-5) M), 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), and ethoxzolamide. These data suggest that C. macularius relies on a low-affinity Na(+)-H(+) exchanger for apical Na(+) uptake and that H(+) ions generated via carbonic anhydrase-mediated CO2 hydration are important for the function of this protein.
本研究对濒危的花鳉（Cyprinodon macularius）在咸淡水环境中的钠离子摄取进行了初步表征。该物种仅分布于美国西南部和墨西哥北部的几个咸水系统中，这些地区的盐度在很大程度上受水资源管理措施控制。因此，了解该物种的渗透调节能力对其保护具有重要意义。研究发现，花鳉在淡水中的最低适应极限为2 mM钠离子。适应2 mM或7 mM钠离子的鱼表现出相似的钠离子摄取动力学，米氏常数（Km）分别为4321和3672 μM，最大反应速度（Vmax）分别为4771和3602 nmol g⁻¹ h⁻¹。一系列使用药理学抑制剂的实验表明，花鳉的钠离子摄取对布美他尼、美托拉宗或苯那普利不敏感。这些结果表明，在适应2 mM或7 mM钠离子的鱼的鳃离子细胞顶端膜上，钠 - 钾 - 2氯共转运体、钠 - 氯共转运体以及钠通道 - 氢 - ATP酶系统可能不参与钠离子摄取。然而，钠离子摄取对1×10⁻³ M氨氯吡脒（而非1×10⁻⁴或1×10⁻⁵ M）、5 - （N - 乙基 - N - 异丙基） - 氨氯吡脒（EIPA）和乙氧唑胺敏感。这些数据表明，花鳉依赖低亲和力的钠 - 氢交换体进行顶端钠离子摄取，并且通过碳酸酐酶介导的二氧化碳水合作用产生的氢离子对该蛋白的功能很重要。
