Bystriansky J S, Frick N T, Ballantyne J S
Department of Biochemistry and Molecular Genetics, University of Illinois, Chicago, IL 60607 USA.
J Exp Biol. 2007 Jun;210(Pt 11):1971-85. doi: 10.1242/jeb.000059.
The migration of Arctic char Salvelinus alpinus from freshwater to seawater requires a substantial reorganization of the osmoregulatory tissues to regulate plasma ion levels. These modifications have an inherent metabolic cost, which must be met through the upregulation of intermediary metabolism. Arctic char intermediary metabolism was monitored during the initial 96 h of seawater acclimation through measurement of key enzymes in gill, liver, red and white muscle as well as tissue and blood free amino acid (FAA) levels, and plasma glucose and non-esterified fatty acid content. In general, seawater exposure stimulated large changes in amino acid metabolism, but no change in lipid or carbohydrate metabolism. White muscle FAA content increased significantly following seawater exposure, with levels of essential FAAs doubling after 96 h. Similar increases were seen in the plasma, suggesting a rapid mobilization of FAAs to the circulation. These changes were accompanied by significant increases in the activities of enzymes involved in amino acid metabolism in the gill, liver, red and white muscle, suggesting seawater-acclimated fish have an enhanced capacity for energy production from amino acids. Increased energy requirements were evident in the gill of seawater-acclimated char, as citrate synthase activity increased significantly. The results of this study suggest a rapid upregulation of amino acid metabolism may be critical for the successful acclimation of Arctic char to seawater.
北极红点鲑（Salvelinus alpinus）从淡水向海水的洄游需要对渗透调节组织进行大量重组，以调节血浆离子水平。这些改变具有内在的代谢成本，必须通过上调中间代谢来满足。在海水驯化的最初96小时内，通过测量鳃、肝脏、红肌和白肌中的关键酶以及组织和血液中的游离氨基酸（FAA）水平、血浆葡萄糖和非酯化脂肪酸含量，对北极红点鲑的中间代谢进行了监测。总体而言，海水暴露刺激了氨基酸代谢的巨大变化，但脂质或碳水化合物代谢没有变化。海水暴露后，白肌FAA含量显著增加，96小时后必需FAA水平翻倍。血浆中也出现了类似的增加，表明FAA迅速动员到循环中。这些变化伴随着鳃、肝脏、红肌和白肌中参与氨基酸代谢的酶活性显著增加，表明适应海水的鱼类从氨基酸产生能量的能力增强。适应海水的红点鲑的鳃中能量需求增加很明显，因为柠檬酸合酶活性显著增加。这项研究的结果表明，氨基酸代谢的快速上调可能对北极红点鲑成功适应海水至关重要。
