A mechanism for branchial acid excretion in marine fish: identification of multiple Na+/H+ antiporter (NHE) isoforms in gills of two seawater teleosts.
A mechanism for branchial acid excretion in marine fish: identification of multiple Na+/H+ antiporter (NHE) isoforms in gills of two seawater teleosts.
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发表时间：
1999-02
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通讯作者：
J. B. Claiborne;C. Blackston;Keith P. Choe;D. C. Dawson;S. Harris;L. Mackenzie;A. Morrison-Shetlar
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作者：
J. B. Claiborne;C. Blackston;Keith P. Choe;D. C. Dawson;S. Harris;L. Mackenzie;A. Morrison-Shetlar
据推测，Na+/H+ 交换和通过 H+-ATP 酶产生的 H+ 电排出可驱动鱼类鳃上皮的酸排泄。虽然 H+-ATPase/Na+ 通道系统似乎是一些淡水物种的主要机制，但它在海水和咸水动物中的作用可能会减弱，因为在这些动物中，高外部 Na+ 浓度可能在热力学上有利于由 Na+/H+ 逆向转运蛋白 (NHE) 驱动的 Na+/H+ 交换。在这项研究中，我们使用分子和免疫学方法来评估 NHE 亚型在海洋长角杜父鱼 (Myoxocephalus octodecimspinosus) 和广盐鳉鱼 (Fundulusheteroclitus) 鳃上皮中的作用。用人 NHE-1 BamHI 片段探测的 RNA 的 Northern 印迹分析表明，杜父鱼中存在同源的鳃 NHE mRNA。 RT-PCR 对从代谢性酸中毒恢复的杜父鱼中分离出的鳃 RNA 进行了 RT-PCR，为两种不同的 NHE 亚型提供了证据；其中一种与哺乳动物 NHE-2 具有 76% 的氨基酸同源性，另一种与鳟鱼红细胞 β-NHE 具有 92% 的同源性。鳉鱼的转录本与 beta-NHE 具有 91% 的同源性。使用哺乳动物 NHE-1 的单克隆抗体进行免疫学检测，发现这两个物种的鳃中都存在与该异构体抗原相似的蛋白质。代谢性酸中毒导致杜父鱼中 NHE-1 样蛋白的表达减少约 30 倍。我们推测鳃中的 β-NHE 发挥着哺乳动物 NHE-1 所描述的细胞内“管家”作用。在全身性酸中毒期间，顶端鳃NHE-2（对外部阿米洛利和低[Na+]敏感）与基底外侧NHE-1活性的显着抑制同时增强净capdelta H+向水中的转移。
Both Na+/H+ exchange and the electrogenic extrusion of H+ via an H+-ATPase have been postulated to drive acid excretion across the branchial epithelium of fishes. While the H+-ATPase/Na+ channel system appears to be the predominant mechanism in some freshwater species, it may play a reduced role in seawater and brackish-water animals, where high external Na+ concentrations may thermodynamically favor Na+/H+ exchange driven by a Na+/H+ antiporter (NHE). In this study, we used molecular and immunological methods to assess the role of NHE isoforms in the branchial epithelium of the marine long-horned sculpin (Myoxocephalus octodecimspinosus) and the euryhaline killifish (Fundulus heteroclitus). Northern blot analysis of RNA probed with the human NHE-1 BamHI fragment suggested the presence of homologous gill NHE mRNA in sculpin. RT-PCR on gill RNA isolated from sculpin recovering from metabolic acidosis provided evidence for two distinct NHE isoforms; one with 76 % amino acid homology to mammalian NHE-2, and another 92 % homologous to trout erythrocytic beta-NHE. Killifish also have transcripts with 91 % homology to beta-NHE. Immunological detection using monoclonal antibodies for mammalian NHE-1 revealed a protein antigenically similar to this isoform in the gills of both species. Metabolic acidosis caused an approximately 30-fold decrease in expression of the NHE-1-like protein in sculpin. We speculate that beta-NHE in the gills plays the intracellular 'housekeeping' roles described for mammalian NHE-1. During systemic acidosis, apical gill NHE-2 (which is sensitive to external amiloride and low [Na+]) in parallel with a dramatic suppression of basolateral NHE-1 activity enhances net capdelta H+ transfers to the water.