CELLULAR MAGNESIUM ION HOMEOSTASIS IN THE MYOCARDIUM

在上一个资助期内和由其他机构进行的研究 实验室表明，特定的激素刺激或细胞内 信号迅速从心肌细胞(或其他细胞)中动员大量的镁离子 细胞)到细胞外空间，反之亦然。另一方面， 得到实验数据支持的普遍理解是，假设 胞内游离镁离子保持相对恒定在毫摩尔- 亚毫米尔级浓度。 因此，该组件项目研究的主要假设是 证明荷尔蒙对心肌细胞的刺激导致心肌细胞的重新分布 胞内细胞器和胞外空间之间的镁离子，离开 胞内镁离子基本不变。这一假设的关键是 证明特定的细胞内信号诱导大量的 跨细胞器，如线粒体、肌浆网和 胞浆，并且这些通量与强大的 肌膜镁离子转运蛋白(S)。 提出的五个具体目标将界定 心肌细胞转运镁离子的各种机制 肌膜、肌浆网和线粒体。其中的一些目标 提出了一项广泛而系统的调查，而其他人则非常 具体的。后者的一个例子是对营地的调查。 与腺核苷酸转位酶的两种同工酶和 当cAMP结合时，导致线粒体的镁-三磷酸腺苷转运。 各种模型(麻醉动物、灌流心脏、心肌细胞、 纯化的其他分离细胞、通透性细胞、分离细胞器 蛋白质、脂质体)和实验方法(31P核磁共振、电子探针 微量分析、细胞成像、同位素、电位测量技术)将 用于确认或整合已获得的有关心肌细胞镁离子的知识 动态平衡。 在目标1中，通过从以下来源获得的信息提出了额外的整合 用麻醉的动物做实验。使用此模型，总体上 镁离子在组织和血浆中重新分配的结果和后果 将会被调查。 最后，与该计划项目的其他研究人员合作， 镁离子在心肌细胞内重新分布的结果及其在心肌细胞中的变化 细胞器的镁离子将与细胞器的功能或 心肌细胞的三磷酸腺苷合成利用和离子调节 渐变。

Studies conducted during the previous funding period and by other laboratories indicate that specific hormonal stimulation or intracellular signals rapidly mobilize large amounts of Mg2+ from myocytes (or other cells) to the extracellular space, and vice versa. On the other hand, the general understanding, supported by experimental data, assumes that cytosolic free Mg2+ is held relatively constant at a millimolar- submillimolar concentration. Hence, the main hypothesis of the research of this Component Project is to demonstrate that hormonal stimulation of myocytes induces redistribution of Mg2+ between intracellular organelles and the extracellular space, leaving cytosolic Mg2+ virtually unchanged. Key to athe hypothesis is the demonstration that specific intracellular signals induce large fluxes of Mg2+ across organelles such as mitochondria, sarcoplasmic reticulum and the cytosol, and that these fluxes are coupled with the activation of powerful sarcolemma Mg2+ transporter(s). The five specific aims proposed will define the operation and regulation of various mechanisms used by the myocardial cell to translocate Mg2+ across the sarcolemma, sarcoplasmic reticulum and mitochondria. Some of the aims proposed a broad and systemic investigation, whereas others are very specific. One example of the latter is the investigation of the cAMP binding to two isozymes of the adenine nucleotide translocase and the resulting Mg-ATP transport from mitochondrial when cAMP is bound. A large variety of models (anesthetized animals, perfused hearts, myocytes, other isolated cells, permeabilized cells, isolated organelles, purified proteins, liposomes) and experimental approaches (31P NMR, Electron Probe Microanalysis, cell imaging, isotopic, potentiometric techniques) will be used to confirm or to integrate the acquired knowledge on myocyte Mg2+ homeostasis. Additional integration is proposed in Aim 1 by information derived from experiments using anesthetized animals. Using this model, the overall results and consequences of Mg2+ redistribution between tissues and plasma will be investigated. Finally, in collaboration with other investigators of this Program Project, the results of Mg2+ redistribution within the myocyte and the changes in organelle Mg2+ will be correlated with the function of the organelles or myocytes in terms of ATP synthesis and utilization, and regulation of ion gradients.