The distal convoluted tubule is mainly responsible for the reabsorption of water and sodium. It regulates pH through the absorption of bicarbonate and secretion of protons (H+) into the filtrate. Sodium absorption by the distal tubule is regulated by the hormone aldosterone. It also takes part in calcium regulation by secretion of excess Ca2+.
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.
Distal Convoluted Tubule