Regulation of magnesium reabsorption in DCT

The distal convoluted tubule (DCT) is the shortest segment of the nephron and consists of an early (DCT1) and late part (DCT2). Here, several transport proteins, like the thiazide-sensitive NaCl cotransporter (NCC) and the epithelial magnesium (Mg2+) channel (TRPM6), are exclusively expressed. This makes the DCT the major site of active transcellular Mg2+ reabsorption determining the final excretion in the urine. Following the Mg2+ influx via the apically localized TRPM6, intracellular Mg2+ diffuses to the basolateral membrane where it is extruded to the blood compartment via still-unidentified Mg2+ transporters. Recent years have witnessed multiple breakthroughs in the field of transcellular Mg2+ reabsorption. Epidermal growth factor and estrogen were identified as magnesiotropic hormones by their effect on TRPM6 activity. Intracellularly, receptor of activated protein kinase C 1 and adenosine triphosphate were shown to inhibit TRPM6 activity through its alpha-kinase domain. Furthermore, dysregulation or malfunction of transcellular Mg2+ reabsorption in DCT has been associated with renal Mg2+ wasting. Mutations in TRPM6 are responsible for hypomagnesemia with secondary hypocalcemia. A defect in the gamma-subunit of the Na+/K+-adenosine triphosphatase causes isolated dominant hypomagnesemia resulting from renal Mg2+ wasting. Moreover, in Gitelman's syndrome, mutations in NCC also result in impaired transcellular Mg2+ reabsorption in DCT. This review highlights our recently obtained knowledge concerning the molecular regulation of transcellular Mg2+ reabsorption.