In zebrafish (Danio rerio), a specific ionocyte subtype, the H⁺-ATPase-rich (HR) cell, is presumed to be a significant site of transepithelial Na⁺ uptake/acid-secretion. During acclimation to environments differing in ionic composition or pH, ionic and acid-base regulation are achieved by adjustments to the activity level of HR cell ion transport proteins. In previous studies, the quantitative assessment of mRNA levels for genes involved in ionic and acid-base regulation relied on measurements using homogenates derived from whole body (larvae) or gill (adult). Such studies cannot distinguish whether any differences in gene expression arise from adjustments of ionocyte subtype numbers, or transcriptional regulation specifically within individual ionocytes. The goal of the present study was to use florescence activated cell sorting (FACS) to separate the HR cells from other cellular sub-populations to facilitate the measurement of gene expression of HR cell-specific transporters and enzymes from larvae exposed to low pH (pH 4.0) or low Na⁺ (5 μM) conditions. The data demonstrate that treatment of larvae with acidic water for 4 days post fertilization caused cell-specific increases in H⁺ATPase (atp6v1aa), ca17a, ca15a, nhe3b and rhcgb mRNA in addition to increases in mRNA linked to cell proliferation. In fish exposed to low Na⁺, expression of nhe3b and rhcgb was increased owing to HR cell-specific regulation as well as elevated numbers of HR cells. Thus, the results of this study demonstrate that acclimation to low pH or low Na⁺ environmental conditions is facilitated by HR cell-specific transcriptional control and by HR cell proliferation.

中文翻译：

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从暴露于酸性或缺钠水的斑马鱼幼虫 (Danio rerio) 分离的离子细胞中离子转运基因的表达。

在斑马鱼 (Danio rerio) 中，一种特定的离子细胞亚型，即富含H ⁺ -ATP 酶 (HR) 的细胞，被认为是跨上皮 Na ⁺的重要部位摄取/酸分泌。在适应不同离子组成或 pH 值的环境期间，通过调节 HR 细胞离子转运蛋白的活性水平来实现离子和酸碱调节。在以前的研究中，参与离子和酸碱调节的基因的 mRNA 水平的定量评估依赖于使用来自全身（幼虫）或鳃（成虫）的匀浆的测量。此类研究无法区分基因表达的任何差异是否源于离子细胞亚型数量的调整，或特定于单个离子细胞内的转录调控。⁺ (5 μM) 条件。数据表明，受精后用酸性水处理幼虫 4 天，导致 H ⁺ ATPase (atp6v1aa)、ca17a、ca15a、nhe3b 和 rhcgb mRNA 的细胞特异性增加，以及与细胞增殖相关的 mRNA 增加。在暴露于低 Na ^{+ 的}鱼中，由于 HR 细胞特异性调节以及 HR 细胞数量增加，nhe3b 和 rhcgb 的表达增加。因此，本研究的结果表明，HR 细胞特异性转录控制和 HR 细胞增殖促进了对低 pH 或低 Na ⁺环境条件的适应。