Glucose metabolism in aquatic animals

水生动物的糖代谢研究已经进行了100多年，但仍有许多重要问题有待解决。1)大西洋鳕鱼气腺葡萄糖代谢。许多鱼利用充满气体的鱼鳔来保持中性浮力。当鱼类潜水时，每10米深度压力增加1大气压。这导致鱼鳔压缩，为了保持浮力，增加的气体必须沉积。在大多数物种中，鱼鳔主要通过聚集在血管网络周围的气体腺充满氧气。腺细胞产生H+，使O2从血红蛋白中释放出来。H+和O2在血浆中积累，O2通过扩散进入鱼鳔。氢离子由厌氧糖酵解产生，同时产生乳酸。关于鱼鳔和气腺功能的生理生化研究很多，但没有一个是在现实生活中发生的压力下进行的。本实验将首次探讨在生理相关条件下气体沉积和葡萄糖代谢的生物化学。新的实验将有可能使用一个新建造的腔室，该腔室能够在控制温度下通过水流产生300大气压的压力。Cod将被利用，因为它们有一个分离的气体压盖，很容易收获。鳕鱼可在2小时内游50至275米，也可出现在500米以上的深度。工作将集中在葡萄糖代谢的第一个关键步骤，即通过葡萄糖转运蛋白1转运到细胞中，并通过己糖激酶磷酸化葡萄糖。该计划的目标将是评估葡萄糖代谢的重要性，并在正常压力变化的动物气腺过程的控制。2)维持细胞内pH值需要细胞外葡萄糖吗？某些鱼类的心脏（如盔甲鲶鱼、白鲟鱼）能够在细胞外pH值降低的情况下维持细胞内pH值，从而维持收缩。pH防御机制尚不清楚，但可能与Na+交换有关，Na+/K+ atp酶（NKA）需要Na+/K+ atp酶来维持Na+平衡。在哺乳动物心脏中，NKA主要通过糖酵解获得能量。在鱼的心脏中，即使在正常的氧气条件下，细胞外葡萄糖也主要（如果不是唯一）用于乳酸的产生，这表明糖酵解的必要性与为膜atp酶提供燃料一致。这就产生了厌氧糖酵解对于维持pHi是必要的假设。心脏细胞将从鱼中分离出来，并暴露在含有或不含葡萄糖的低pHe培养基中。将跟踪pHi、耗氧量、乳酸生成和葡萄糖代谢。这个程序将阐明葡萄糖代谢的作用，这是特定的特定功能，而不是作为ATP生产的一般燃料来源。这将导致我们如何看待葡萄糖的作用的范式转变。

Glucose metabolism has been studied in aquatic animals for over 100 years yet there remain important questions to be resolved. 1) Glucose metabolism in Atlantic cod gas gland. Many fish utilize a gas filled swim bladder to maintain neutral buoyancy. As fish dive pressure increases by 1 atm for every 10 m of depth. This causes the swim bladder to compress and in order to maintain buoyancy increased gas must be deposited. In most species the swim bladder is filled primarily with O2 via a gas gland that clusters around a network of blood vessels. The glandular cells generate H+ that causes O2 to unload from haemoglobin. H+ and O2 accumulate in the plasma and O2 moves by diffusion into the swim bladder. H+ is produced from anaerobic glycolysis with the production of lactic acid. There are many studies on the physiology and biochemistry of swim bladder and gas gland function but none have been conducted at pressures that occur in real life. The present experiments will address for the first time the biochemistry of gas deposition and glucose metabolism under physiologically relevant conditions. Novel experiments will be possible with the use of a newly constructed chamber that is capable of developing pressures of 300 atm with flow through water at controlled temperatures. Cod will be utilized since they have a discrete gas gland that is easy to harvest. Cod may travel between 50 and 275 m in 2 hr and may also occur at depths greater than 500 m. Work will focus on the first critical steps in glucose metabolism, i.e. transport into the cell via glucose transporter 1 and phosphorylation of glucose by hexokinase. The objectives of the program will be to assess the importance of glucose metabolism and control of the process in gas gland in animals undergoing normal pressure changes. 2) Is extracellular glucose required to maintain intracellular pH? Hearts from some species of fish (e.g. Armoured catfish, white sturgeon) are able to maintain intracellular pH at decreased extracellular pH allowing maintenance of contraction. The mechanisms of pH defense are unknown but likely involve Na+ exchange which places demands on Na+/K+ ATPase (NKA) to maintain Na+ balance. In mammalian heart, NKA is fueled primarily by glycolysis. In fish hearts, extracellular glucose is directed primarily if not exclusively to lactate production even under normal O2, suggesting a necessity for glycolysis consistent with fueling membrane ATPases. This leads to the hypothesis that anaerobic glycolysis is necessary to maintain pHi. Heart cells will be isolated from fish and exposed to low pHe with or without glucose in the medium. pHi, oxygen consumption, lactate production, and glucose metabolism will be tracked. This program will articulate roles of glucose metabolism that are specific to particular functions as opposed to being a general fuel source for ATP production. This will result in a paradigm shift with respect to how we think about the role of glucose..