CELLULAR MAGNESIUM AND CALCIUM ION HOMEOSTASIS IN HEART

尽管体内和组织内Mg2+含量丰富，但对细胞和血浆Mg2+稳态的调节知之甚少。在过去九年的研究中，该项目以及许多其他实验室的研究表明，细胞Mg2+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代谢方面发挥新作用。特定的激素刺激和细胞内第二信使水平的变化诱导大量Mg2+从心脏转运到细胞外环境并最终进入血液，反之亦然。本研究继续使用多种模型（灌注心脏、肌细胞、其他分离细胞、渗透细胞、分离细胞器、纯化蛋白）和实验方法（31P NMR、电子探针、微量分析、细胞成像、同位素电位测定技术）来获取或整合心脏中MG1+稳态的知识。本应用的目的是验证几个主要假设：在肌细胞中有多种Mg2+转运体介导Mg2+的摄取和释放，以及激活和抑制Mg2+转运的信号通路的冗余。细胞Mg2+释放可能是α 1或β肾上腺素能反应的主要部分。肌细胞的Mg2+外排增加了心肌间质Mg2+浓度并刺激腺苷的产生。在心脏中，Mg2+大量外排的一部分通过一种新的Mg2+-Ca2+反转运体与Ca2+摄取相结合，因此，儿茶酚胺刺激的Mg2+外排可能是Ca2+进入的另一途径。Mg2+在心脏和其他组织中的积累不受细胞外Mg2+的影响，而是通过蛋白激酶C的特定信号通路独立调节。

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.