Disorders of Magnesium: Physiology

Abstract

Magnesium (Mg²⁺) is the second most common intracellular cation next to K⁺ in the body. A 70-kg individual has approximately 25 g of Mg²⁺. About 67 % of this Mg²⁺ is present in bone, about 20 % in muscle, and 12 % in other tissues such as the liver. Only 1–2 % is present in the extracellular space. In plasma, Mg²⁺ exists as free (60 %) and bound (40 %) forms. About 10 % is bound to HCO₃ ⁻, citrate, and phosphate and 30 % to albumin. Only the free and nonprotein-bound Mg²⁺ is filtered at the glomerulus. Mg²⁺ plays an essential role in cellular metabolism. It is involved in activation of enzymes such as phosphokinases and phosphatases. Mg-ATPase is also involved in the hydrolysis of ATP and thus the generation of energy that is utilized in several ion-pump activities. In addition, Mg²⁺ plays a critical role in protein synthesis and cell volume regulation. Because of its pivotal role in cellular physiology, Mg²⁺ deficiency adversely affects many cellular functions.