Distribution of magnesium in the arterial wall

1. The Mg, Ca, Na and K content were determined in the rat tail artery in vitro under various experimental conditions. 2. The arterial Mg could be varied selectively at a constant [Mg] o by altering the content of intracellular compounds capable of forming complexes with Mg 2+ such as nucleoside‐5′‐triphosphates or citrate. 3. The release of tissue Mg during incubation in Mg‐free solutions was found to consist of a fast and a slow component. The size of the fast component was dependent on the original [Mg] o . The size of the slow component was dependent on the content of intracellular compounds forming complexes with Mg 2+ . The rate of efflux of the slow component could be increased by increasing [Mg 2+ ] i , by removing external Ca, or by making the artery metabolically inactive. 4. The results seem to indicate that [Mg 2+ ] i in metabolically active vascular smooth muscle cells is maintained at a level of ca . 10 −4 M .