Takvam Marius, Wood Chris M, Kryvi Harald, Nilsen Tom O
Department of Biological Sciences, University of Bergen, Bergen, Norway.
NORCE, Norwegian Research Centre, NORCE Environment, Bergen, Norway.
Front Physiol. 2021 Apr 20;12:664588. doi: 10.3389/fphys.2021.664588. eCollection 2021.
Euryhaline teleosts exhibit major changes in renal function as they move between freshwater (FW) and seawater (SW) environments, thus tolerating large fluctuations in salinity. In FW, the kidney excretes large volumes of water through high glomerular filtration rates (GFR) and low tubular reabsorption rates, while actively reabsorbing most ions at high rates. The excreted product has a high urine flow rate (UFR) with a dilute composition. In SW, GFR is greatly reduced, and the tubules reabsorb as much water as possible, while actively secreting divalent ions. The excreted product has a low UFR, and is almost isosmotic to the blood plasma, with Mg, SO , and Cl as the major ionic components. Early studies at the organismal level have described these basic patterns, while in the last two decades, studies of regulation at the cell and molecular level have been implemented, though only in a few euryhaline groups (salmonids, eels, tilapias, and fugus). There have been few studies combining the two approaches. The aim of the review is to integrate known aspects of renal physiology (reabsorption and secretion) with more recent advances in molecular water and solute physiology (gene and protein function of transporters). The renal transporters addressed include the subunits of the Na, K- ATPase (NKA) enzyme, monovalent ion transporters for Na, Cl, and K (NKCC1, NKCC2, CLC-K, NCC, ROMK2), water transport pathways [aquaporins (AQP), claudins (CLDN)], and divalent ion transporters for SO , Mg, and Ca (SLC26A6, SLC26A1, SLC13A1, SLC41A1, CNNM2, CNNM3, NCX1, NCX2, PMCA). For each transport category, we address the current understanding at the molecular level, try to synthesize it with classical knowledge of overall renal function, and highlight knowledge gaps. Future research on the kidney of euryhaline fishes should focus on integrating changes in kidney reabsorption and secretion of ions with changes in transporter function at the cellular and molecular level (gene and protein verification) in different regions of the nephrons. An increased focus on the kidney individually and its functional integration with the other osmoregulatory organs (gills, skin and intestine) in maintaining overall homeostasis will have applied relevance for aquaculture.
广盐性硬骨鱼在淡水（FW）和海水（SW）环境之间移动时，肾功能会发生重大变化，从而能够耐受盐度的大幅波动。在淡水中，肾脏通过高肾小球滤过率（GFR）和低肾小管重吸收率排出大量水分，同时以高速率主动重吸收大多数离子。排出的产物具有高尿流率（UFR）且成分稀释。在海水中，GFR大幅降低，肾小管尽可能多地重吸收水分，同时主动分泌二价离子。排出的产物具有低UFR，并且几乎与血浆等渗，主要离子成分是镁、硫酸根和氯离子。早期在生物体水平的研究描述了这些基本模式，而在过去二十年中，虽然仅在少数广盐性鱼类群体（鲑科鱼类、鳗鱼、罗非鱼和河豚）中开展了细胞和分子水平的调节研究，但已实施了相关研究。将这两种方法结合起来的研究很少。本综述的目的是将肾脏生理学的已知方面（重吸收和分泌）与分子水平的水和溶质生理学的最新进展（转运蛋白的基因和蛋白质功能）整合起来。所涉及的肾脏转运蛋白包括钠钾ATP酶（NKA）的亚基、钠、氯和钾的单价离子转运蛋白（NKCC1、NKCC2、CLC-K、NCC、ROMK2）、水转运途径[水通道蛋白（AQP）、紧密连接蛋白（CLDN）]以及硫酸根、镁和钙的二价离子转运蛋白（SLC26A6、SLC26A1、SLC13A1、SLC41A1、CNNM2、CNNM3、NCX1、NCX2、PMCA）。对于每一类转运，我们阐述了分子水平的当前认识，试图将其与肾脏整体功能的经典知识相结合，并突出知识空白。未来对广盐性鱼类肾脏的研究应侧重于将肾脏离子重吸收和分泌的变化与肾单位不同区域细胞和分子水平（基因和蛋白质验证）的转运蛋白功能变化整合起来。更多地关注肾脏个体及其与其他渗透调节器官（鳃、皮肤和肠道）在维持整体内环境稳态方面的功能整合，将对水产养殖具有实际意义。
