Department of Anatomy and Cell Biology, Taipei Medical University, Taipei, Taiwan.
Department of Life Science, National Taiwan Normal University, Taipei, Taiwan.
Sci Rep. 2017 Nov 24;7(1):16215. doi: 10.1038/s41598-017-16381-7.
Molecular mechanisms of Na, Cl, and Ca regulation in ionocytes of fish have been well investigated. However, the regulatory mechanism of K in fishes has been largely unknown. In this study, we investigated the mechanism of K regulation in medaka larvae acclimated to fresh water. Using a scanning ion-selective electrode technique (SIET) to measure the K fluxes at skin cells, significant K effluxes were found at ionocytes; in contrast, significant K influxes were found at the boundaries between keratinocytes. High K water (HK) acclimation induced the K effluxes at ionocytes and suppressed the K influxes at keratinocytes. The K effluxes of ionocytes were suppressed by VU591, bumetanide and ouabain. The K influxes of keratinocytes were suppressed by TAP. In situ hybridization analysis showed that mRNA of ROMKa was expressed by ionocytes in the skin and gills of medaka larvae. Quantitative PCR showed that mRNA levels of ROMKa and NKCC1a in gills of adult medaka were upregulated after HK acclimation. This study suggests that medaka obtain K through a paracellular pathway between keratinocytes and extrude K through ionocytes; apical ROMKa and basolateral NKCC1a are involved in the K secretion by ionocytes.
鱼类离子细胞中钠、氯和钙的调节分子机制已得到深入研究。然而，鱼类钾的调节机制在很大程度上仍不清楚。本研究通过扫描离子选择性电极技术（SIET）测量皮肤细胞中的钾通量，研究了适应淡水的斑马鱼幼虫中钾的调节机制。结果发现，在离子细胞中有明显的钾外流，而在角蛋白细胞之间的边界处有明显的钾内流；高钾水（HK）适应诱导了离子细胞中的钾外流，并抑制了角蛋白细胞中的钾内流。VU591、布美他尼和哇巴因抑制了离子细胞的钾外流，TAP 抑制了角蛋白细胞的钾内流。原位杂交分析显示，ROMKa mRNA 在斑马鱼幼虫皮肤和鳃中的离子细胞中表达。定量 PCR 显示，HK 适应后，成年斑马鱼鳃中的 ROMKa 和 NKCC1a mRNA 水平上调。本研究表明，斑马鱼通过角蛋白细胞之间的细胞旁途径获取钾，并通过离子细胞排出钾；顶端 ROMKa 和基底外侧 NKCC1a 参与离子细胞的钾分泌。
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