Glucose metabolism in aquatic animals

研究水生动物的葡萄糖代谢已有100多年的历史，但仍有一些重要的问题有待解决。 1)大西洋鳕鱼气腺的葡萄糖代谢。 许多鱼利用充满气体的鱼鳔来保持中性浮力。当鱼下潜时，压力每增加10米就增加1个大气压。这导致鱼鳔压缩，为了保持浮力，必须沉积增加的气体。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体充满氧气。 腺细胞产生H+，导致O 2从血红蛋白中卸载。H+和O2在血浆中积累，O2通过扩散进入鱼鳔。H+是由厌氧糖酵解产生乳酸。 有许多关于鱼鳔和气体腺功能的生理学和生物化学的研究，但没有一个是在真实的生活中发生的压力下进行的。 本实验将首次解决生理相关条件下的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，该腔室能够在受控温度下通过水流产生300个大气压的压力。鳕鱼将被利用，因为他们有一个离散的气体腺，很容易收获。鳕鱼可以在2小时内游50至275米，也可能出现在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转运到细胞中以及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和控制的过程中的气体腺在动物经历正常的压力变化。 2)细胞外葡萄糖是维持细胞内pH所必需的吗？ 某些鱼类（如甲鲶、白色鲟鱼）的心脏能够在细胞外pH降低时维持细胞内pH，从而维持收缩。pH防御的机制尚不清楚，但可能涉及Na+交换，这需要Na+/K+ ATP酶（NKA）来维持Na+平衡。在哺乳动物心脏中，NKA主要通过糖酵解提供能量。在鱼的心脏，细胞外葡萄糖是直接主要的，如果不是唯一的乳酸生产，即使在正常的O2，这表明糖酵解的必要性与燃料膜ATP酶一致。这导致了无氧糖酵解对于维持pHi是必要的假设。将从鱼中分离心脏细胞，并将其暴露于培养基中有或没有葡萄糖的低pH He。 将跟踪pHi、耗氧量、乳酸盐产生和葡萄糖代谢。该计划将阐明葡萄糖代谢的作用，这是特定的功能，而不是作为一个一般的燃料来源ATP生产。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.**********.************