Charge translocation by the sodium-potassium pump in the giant axon of the Humbol

描述（由申请人提供）：钠钾（Na +/K+）泵是一种重要的膜蛋白，其利用ATP的能量逆其电化学梯度转运Na+和K+，以维持细胞稳态。本研究的目的是在分子水平上了解Na +/K+泵运输循环中的离子事件。具体来说，我们的目标是描述和定量的运动的Na+和K+的进出溶液中的结合位点位于泵蛋白。实验包括测量的电荷运动，电压扰动的结果，使用快速电压钳在鱿鱼巨大的轴突。这些实验允许测量从泵释放到外部溶液中的三个Na+离子中的每一个的运动的时间过程。这项建议将在智利蒙特马尔的细胞生理学实验室进行，那里有来自鱿鱼Dosidicus gigas的1毫米轴突。对于这些轴突，电荷运动的信噪比比Loligo pealeii轴突高得多，这将允许使用Loligo轴突不可行的测量。具体目标是：1）了解细胞外Na+转运转换的热力学。我们的目的是研究在钠离子的结合和释放过程中发生的熵和熵的变化，进出泵的外部接入通道。这将通过测量与Na+易位相关的电荷运动的所有三个分量的温度依赖性来完成。2)了解Na +/K+泵的K+转运机制的生物物理特性。这一具体目标需要全面研究涉及K+的运动作为外部K+，电压，细胞内ATP和无机磷酸盐浓度的函数的转换。这些研究预计将提供一个机制和分子的Na +/K+泵介导的电事件，这是一个普遍存在的膜蛋白的健康和疾病的根本重要性。这项研究将主要在智利蒙特马尔与瓦尔帕莱索大学教授Ramon Latorre合作完成，作为NIH资助号R37GM30376 - 29的延伸。公共卫生相关性：这里提出的实验，预计直接测量的离子运动的Na +/K+泵和泵操作过程中提供的离子结合和解结合的生物物理机制。Na +/K+泵的活性对于细胞内稳态至关重要，因为它有助于维持Na+和K+梯度。这在可兴奋细胞中尤其重要，在可兴奋细胞中，负荷在动作电位期间发生变化。在临床上，Na +/K+泵是重要的，因为它是地高辛、洋地黄毒苷和其他强心类固醇的受体。

DESCRIPTION (provided by applicant): The sodium potassium (Na+/K+) pump is an important membrane protein that uses the energy of ATP to transport Na+ and K+ against their electrochemical gradients to maintain cell homeostasis. This study is aimed at the molecular understanding of the ionic events in the Na+/K+ pump transport cycle. Specifically, we aim at the description and quantification of the movements of Na+ and K+ in and out from the solution to the binding sites located within the pump protein. The experiments consist of measuring the charge movement that results from voltage perturbations using a fast voltage clamp in the squid giant axon. These experiments allow the measurement of the time course of the movement of each of the three Na+ ions released from the pump into the external solution. This proposal is to be carried out at the Laboratory of Cellular Physiology in Montemar, Chile, where 1 mm axons from the squid Dosidicus gigas are available. With these axons, the signal-to-noise ratio of the charge movement is much higher than in the Loligo pealeii axons, which will allow measurements that are not feasible with Loligo axons. The specific aims are 1) understand the thermodynamics of extracellular Na+ translocation transitions. We aim at the study of the entropic and enthalpic changes that occur during the binding and release of the Na+ ions in and out of the external access channel of the pump. This will be done by measuring the temperature dependence of all three components of the charge movement associated with the Na+ translocation. 2) Understand the biophysical properties of K+ translocation mechanism of the Na+/K+ pump. This specific aim requires a comprehensive study of transitions involving the movement of K+ as a function of external concentration of K+, voltage, intracellular ATP and inorganic phospate. These studies are expected to give a mechanistic and molecular description of the electrical events mediated by the Na+/K+ pump, which is a ubiquitous membrane protein of fundamental importance in health and disease. This research will be done primarily in Montemar, Chile in collaboration with Ramon Latorre, Professor, Universidad de Valparaiso, as an extension of NIH grant No R37GM30376-29. PUBLIC HEALTH RELEVANCE: The experiments proposed here are expected to give direct measurements of the ion movements in and out of the Na+/K+ pump and provide the biophysical mechanisms of the ion binding and unbinding during the pump operation. The activity of the Na+/K+ pump is vital for cell homeostasis because it helps maintaining the Na+ and K+ gradients. It is especially important in excitable cells where the loads change during the action potential. Clinically, the Na+/K+ pump is important because it is the receptor of digoxin, digitoxin and other cardiotonic steroids.