Romani A M, Scarpa A
Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA.
Front Biosci. 2000 Aug 1;5:D720-34. doi: 10.2741/romani.
The abundance of magnesium (Mg2+) within mammalian cells is consistent with its relevant role in regulating tissue and cell functions. At the last count, more than three hundred and fifty enzymes, aside from metabolic cycles, appear to require and be regulated by concentrations of Mg2+ that are well within the physiological range observed in tissues and cells. The absence of detectable major changes in cellular free [Mg2+], and the extremely slow turn-over of the cation across the cell plasma membrane under quiescent condition has supported for more than three decades the assumption that cellular Mg2+ content is kept constant at the level necessary for enzyme and channel function, and that its concentration does not require drastic and rapid changes to form complex with ATP and other phosphonucleotides. In the last decade, a large body of new experimental observations has significantly reverted this way of thinking. Compelling evidence now suggests that large fluxes of Mg2+ can cross the cell plasma membrane in either direction following a variety of hormonal and non-hormonal stimuli, resulting in major changes in total and, to a lesser extent, free Mg2+ content within tissues, and in a marked variation in the opposite direction of circulating Mg2+ level. The present review will attempt to update our knowledge in this area and provide some insights on how changes in cellular Mg2+ content can result in a modification of the activity rate for several cellular enzymes.
哺乳动物细胞内镁离子（Mg2+）的丰富程度与其在调节组织和细胞功能方面的相关作用相一致。据最新统计，除代谢循环外，超过三百五十种酶似乎需要并受Mg2+浓度的调节，而这些浓度完全处于组织和细胞中观察到的生理范围内。细胞内游离[Mg2+]没有可检测到的重大变化，并且在静止状态下阳离子跨细胞质膜的周转极其缓慢，三十多年来一直支持这样一种假设，即细胞内Mg2+含量保持在酶和通道功能所需的水平恒定，并且其浓度不需要急剧和快速变化就能与ATP和其他磷酸核苷酸形成复合物。在过去十年中，大量新的实验观察结果显著改变了这种思维方式。现在有令人信服的证据表明，在各种激素和非激素刺激后，大量的Mg2+可以双向穿过细胞质膜，导致组织内总Mg2+含量发生重大变化，在较小程度上导致游离Mg2+含量发生变化，并且循环Mg2+水平呈现相反方向的显著变化。本综述将试图更新我们在这一领域的知识，并就细胞内Mg2+含量的变化如何导致几种细胞酶的活性速率改变提供一些见解。
