Hypomagnesemia

Cellular physiology and metabolism of magnesium

Magnesium is a divalent cation (Mg ⁺⁺ ) that is predominantly localized to the intracellular compartment (99%). It is the second most abundant intracellular cation after potassium and plays an important role in cellular metabolism and homeostasis. At the cellular level, Mg ⁺⁺ influences membrane function by regulating ion transport; Mg ⁺⁺ is required for sodium/potassium–adenosine triphosphatase (Na ⁺ /K ⁺ -ATPase) activity, which maintains transmembrane gradients for Na ⁺ and K ⁺ . ^, Mg ⁺⁺ also regulates intracellular calcium (Ca ⁺⁺ ) flux by competing for Ca ⁺⁺ binding sites and influencing intracellular Ca ⁺⁺ transport. ^, It is also an essential cofactor for most ATP-requiring processes. Intracellular Mg ⁺⁺ is required for numerous critical biochemical processes, including DNA synthesis, activation of gene transcription, initiation of protein synthesis, and regulation of energy metabolism. ^,

Total body magnesium (21–28 g) is distributed in bone (53%), muscle (27%), soft tissue (19%), and blood (0.8%). The normal concentration of total magnesium in serum is 1.5–2.3 mg/dL. Approximately 19% of circulating magnesium is bound to proteins, whereas 14% is complexed to plasma anions (citrate, phosphate, and bicarbonate). The majority of magnesium in plasma exists in its ionized form (67%), which represents the physiologically active species. Consequently, the measurements of total serum magnesium may not accurately reflect the relative abundance of circulating Mg ⁺⁺ . ^,

Magnesium homeostasis is maintained by the small intestine, kidney, and bone. ^, Unlike calcium, there are no hormonal mechanisms for regulating Mg ⁺⁺ . Mg ⁺⁺ reabsorption in the loop of Henle is linked to sodium chloride (NaCl) transport and is inversely related to flow. Consequently, diuretic use and other conditions associated with increased tubular flow result in decreased Mg ⁺⁺ reabsorption. ^,