Physiological Reviews, Vol. 81, No. 1, January 2001, pp. 51-84
Copyright ©2001 by the American Physiological Society

Magnesium Transport in the Renal Distal Convoluted Tubule

Department of Medicine, University of British Columbia, Vancouver, British Columbia; and Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada

Dai, Long-Jun, Gordon Ritchie, Dirk Kerstan, Hyung Sub Kang, David E. C. Cole, and Gary A. Quamme. Magnesium Transport in the Renal Distal Convoluted Tubule. Physiol. Rev. 81: 51-84, 2001.The distal tubule reabsorbs ~10% of the filtered Mg²⁺, but this is 70-80% of that delivered from the loop of Henle. Because there is little Mg²⁺ reabsorption beyond the distal tubule, this segment plays an important role in determining the final urinary excretion. The distal convoluted segment (DCT) is characterized by a negative luminal voltage and high intercellular resistance so that Mg²⁺ reabsorption is transcellular and active. This review discusses recent evidence for selective and sensitive control of Mg²⁺ transport in the DCT and emphasizes the importance of this control in normal and abnormal renal Mg²⁺ conservation. Normally, Mg²⁺ absorption is load dependent in the distal tubule, whether delivery is altered by increasing luminal Mg²⁺ concentration or increasing the flow rate into the DCT. With the use of microfluorescent studies with an established mouse distal convoluted tubule (MDCT) cell line, it was shown that Mg²⁺ uptake was concentration and voltage dependent. Peptide hormones such as parathyroid hormone, calcitonin, glucagon, and arginine vasopressin enhance Mg²⁺ absorption in the distal tubule and stimulate Mg²⁺ uptake into MDCT cells. Prostaglandin E₂ and isoproterenol increase Mg²⁺ entry into MDCT cells. The current evidence indicates that cAMP-dependent protein kinase A, phospholipase C, and protein kinase C signaling pathways are involved in these responses. Steroid hormones have significant effects on distal Mg²⁺ transport. Aldosterone does not alter basal Mg²⁺ uptake but potentiates hormone-stimulated Mg²⁺ entry in MDCT cells by increasing hormone-mediated cAMP formation. 1,25-Dihydroxyvitamin D₃, on the other hand, stimulates basal Mg²⁺ uptake. Elevation of plasma Mg²⁺ or Ca²⁺ inhibits hormone-stimulated cAMP accumulation and Mg²⁺ uptake in MDCT cells through activation of extracellular Ca²⁺/Mg²⁺-sensing mechanisms. Mg²⁺ restriction selectively increases Mg²⁺ uptake with no effect on Ca²⁺ absorption. This intrinsic cellular adaptation provides the sensitive and selective control of distal Mg²⁺ transport. The distally acting diuretics amiloride and chlorothiazide stimulate Mg²⁺ uptake in MDCT cells acting through changes in membrane voltage. A number of familial and acquired disorders have been described that emphasize the diversity of cellular controls affecting renal Mg²⁺ balance. Although it is clear that many influences affect Mg²⁺ transport within the DCT, the transport processes have not been identified.