Beyenbach K W
Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA.
Front Biosci. 2000 Aug 1;5:D712-9. doi: 10.2741/beyenbach.
Of all known vertebrate tissues, the kidneys of fish are the champions of Mg transport. They can switch from Mg conservation in fresh water to Mg wasting in seawater. High rates of tubular transport and the ability to alternate between Mg reabsorption and secretion make fish kidneys the model of choice investigating the mechanisms of transepithelial and membrane Mg transport and its regulation by extracellular hormones and intracellular messengers. Studies in isolated proximal tubules indicate active transepithelial Mg transport that requires metabolic energy for both tubular reabsorption and secretion. Whether active transport is primary and mediated by a Mg-pump, or secondary and mediated via cotransport or antiport, is unknown. In fresh water fish, the active transport pathway appears to include a Mg-channel located in brush-border membranes of proximal tubules. Although plasma Mg concentrations are well protected, a primary hormone controlling Mg balance has yet to be identified in any animal. Moreover, the mechanisms of intracellular Mg homeostasis, especially in epithelial cells with high Mg throughput, are unknown. New methods, including Mg imaging and genetic/molecular approaches promise to unravel Mg transport mechanisms in teleost renal tubules.
在所有已知的脊椎动物组织中，鱼类的肾脏是镁转运的佼佼者。它们能够从在淡水中保存镁转变为在海水中排出镁。肾小管的高转运速率以及在镁重吸收和分泌之间交替的能力，使鱼类肾脏成为研究跨上皮和膜镁转运机制以及细胞外激素和细胞内信使对其调节的首选模型。对分离的近端小管的研究表明，存在活跃的跨上皮镁转运，肾小管的重吸收和分泌都需要代谢能量。主动转运是由镁泵介导的原发性转运，还是通过协同转运或反向转运介导的继发性转运，目前尚不清楚。在淡水鱼中，主动转运途径似乎包括位于近端小管刷状缘膜上的镁通道。尽管血浆镁浓度受到很好的保护，但尚未在任何动物中鉴定出控制镁平衡的主要激素。此外，细胞内镁稳态的机制，尤其是在镁通量高的上皮细胞中的机制，尚不清楚。包括镁成像和基因/分子方法在内的新方法有望揭示硬骨鱼肾小管中的镁转运机制。
