What is different about kidney magnesium handling from other electrolytes?
Unlike most other electrolytes, where absorption takes place in the proximal tubule, magnesium reabsorption occurs predominantly at the thick ascending limb of the loop of Henle (TAH). That being said, roughly 20% of filtered magnesium is reabsorbed in the proximal tubule. About 70% of the filtered magnesium is absorbed in the thick ascending loop of Henle. This occurs through paracellular tight junctions down the electrical gradient. The electrical gradient is established by the renal outer medullary potassium (ROMK) channel, which allows intracellular potassium to flow into the tubule. Potassium is the rate-limiting reagent for the sodium, potassium, two chloride (NK2Cl) channel