Human geneSLC41A1encodes for the Na+/Mg2+exchanger

Abstract

Magnesium (Mg2+), the second most abundant divalent intracellular cation, is involved in the vast majority of intracellular processes, including the synthesis of nucleic acids, proteins, and energy metabolism. The concentration of intracellular free Mg2+([Mg2+]i) in mammalian cells is therefore tightly regulated to its optimum, mainly by an exchange of intracellular Mg2+for extracellular Na+. Despite the importance of this process for cellular Mg2+homeostasis, the gene(s) encoding for the functional Na+/Mg2+exchanger is (are) still unknown. Here, using the fluorescent probe mag-fura 2 to measure [Mg2+]ichanges, we examine Mg2+extrusion from hSLC41A1-overexpressing human embryonic kidney (HEK)-293 cells. A three- to fourfold elevation of [Mg2+]iwas accompanied by a five- to ninefold increase of Mg2+efflux. The latter was strictly dependent on extracellular Na+and reduced by 91% after complete replacement of Na+with N-methyl-d-glucamine. Imipramine and quinidine, known unspecific Na+/Mg2+exchanger inhibitors, led to a strong 88% to 100% inhibition of hSLC41A1-related Mg2+extrusion. In addition, our data show regulation of the transport activity via phosphorylation by cAMP-dependent protein kinase A. As these are the typical characteristics of a Na+/Mg2+exchanger, we conclude that the human SLC41A1 gene encodes for the Na+/Mg2+exchanger, the predominant Mg2+efflux system. Based on this finding, the analysis of Na+/Mg2+exchanger regulation and its involvement in the pathogenesis of diseases such as Parkinson's disease and hypertension at the molecular level should now be possible.