Extracellular magnesium regulates intracellular free Mg2+ in vascular smooth muscle cells.

Regulatory effects of extracellular magnesium ions ([Mg2+]o) on intracellular free ionized magnesium ([Mg2+]i) were examined in cultured vascular smooth muscle cells (VSMCs) from rat aorta by digital imaging microscopy using the Mg2+ fluorescent probe, Mag-fura-2. With normal Mg2+ (1.2 mM)-containing incubation media, [Mg2+]i in VSMCs was 0.63 +/- 0.09 mM. The ratio of [Mg2+]i/[Mg2+]o was 0.52 +/- 0.07. Elevation of [Mg2+]o up to 4.8 mM induced consistent increments in [Mg2+]i (to a mean values of 1.63 +/- 0.08 mM) in 5 min and lowered the ratio of [Mg2+]i/[Mg2+]o to 0.34 +/- 0.02. Our data suggest that [Mg2+]o can regulate [Mg2+]i, which may be related to its effects on intracellular Ca2+ ([Ca2+]i) and tone of VSMCs.