CELLULAR MAGNESIUM AND CALCIUM ION HOMEOSTASIS IN HEART

尽管体内、体内组织和组织内的镁离子含量丰富，但对细胞和血浆中镁离子稳态的调节知之甚少。该项目以及其他许多实验室在过去九年中进行的研究表明，细胞内镁离子稳态非常活跃，具有复杂和多种形式的调节，并可能直接或间接地在调节细胞功能和新陈代谢方面提供新的作用。特定的激素刺激和细胞内第二信使水平的变化导致大量和快速的镁离子从心脏运输到细胞外环境，最终进入血液，反之亦然。这一建议继续使用各种模型(灌流心脏、心肌细胞、其他分离细胞、通透性细胞、分离细胞器、纯化蛋白质)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)来获取或整合关于心脏MG1+稳态的知识。这一应用的目的是检验几个主要假说：在心肌细胞中，存在多种介导镁摄取和释放的镁离子转运体，以及激活和抑制镁离子转运的信号通路的冗余。这种细胞内镁离子的释放可能是α1或β肾上腺素能反应的主要部分。心肌细胞的镁离子外流增加了心肌间质中的镁离子浓度，刺激腺苷的产生。在心脏中，大量的镁离子外流中的一部分通过一种新的镁-钙逆向转运蛋白与钙摄取偶联，因此，儿茶酚胺刺激的镁离子外流可能是钙离子进入的另一条途径。心脏和其他组织中镁离子的积累不受细胞外镁离子的影响，但通过蛋白激酶C独立地受特定信号通路的调节。

Despite the abundance of Mg2+ in the body and within tissues in the body and within tissues, little is known about the regulation of cellular and plasma Mg2+ homeostasis. Studies conducted during the last nine years of finding to this Project, as well as those many other laboratories, have shown that cellular Mg2+ homeostasis is very active, has sophisticated and multiple forms of regulation and may provide, directly or indirectly, a novel role in regulating cell function and metabolism. Specific hormonal stimulation and changes in intracellular second messenger level induce the transport of large and rapid amounts of Mg2+ from heart into the extracellular milieu and ultimately into the bloodstream, or vice versa. This proposal continues to use a large variety of models (perfused hearts, myocytes, other isolated cells, permeabilized cells, isolated organelles, purified proteins) and experimental approaches (31P NMR, Electron Probe, Microanalysis, cell imaging, isotopic potentiometric techniques to acquire or integrate the knowledge on MG1+ homeostasis in heart. The objective of this application is o test several major hypothesis: That in myocytes there is a multiplicity of Mg2+ transporters mediating Mg2+ uptake and release, as well as a redundancy of signaling pathways activating and inhibiting Mg2+ transport. That cellular Mg2+ release may be a major part of the alpha1 or beta adrenergic response. That Mg2+ efflux from myocytes increases interstitial Mg2+ concentration in the myocardium and stimulates adenosine production. That in the heart a fraction of the large efflux of Mg2+ is coupled to Ca2+ uptake through a novel Mg2+-Ca2+ anti-porter Hence, Mg2+ efflux stimulated by catecholamines may be an additional pathway of Ca2+ entry. That the accumulation of Mg2+ in heart and other tissues is unaffected by extracellular Mg2+ but is independently regulated by specific signaling pathways through protein kinase C.