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.