REVIEW Magnesium is the second most plentiful cation of the intracellular fluids. It is essential for the activity of many enzyme systems and plays an important role with regard to neurochemical transmission and muscular excitability. Magnesium sulfate reduces striated muscle contractions and blocks peripheral neuromuscular transmission by reducing acetylcholine release at the myoneural junction. Additionally, Magnesium inhibits Ca2+ influx through dihydropyridine-sensitive, voltage-dependent channels. This accounts for much of its relaxant action on vascular smooth muscle.
Blitz M, Blitz S, Hughes R, Diner B, Beasley R, Knopp J, Rowe BH: Aerosolized magnesium sulfate for acute asthma: a systematic review. Chest. 2005 Jul;128(1):337-44.