Depolarization triggers intracellular magnesium surge in cultured dorsal root ganglion neurons.

Intracellular magnesium concentration ([Mg2+]i) of cultured dorsal root ganglion (DRG) neurons was measured using the magnesium indicator Mag-Fura-2/AM. [Mg2+]i was 0.48 +/- 0.08 mM (mean +/- SEM, n = 23) at rest, and it increased 3-fold by depolarization with a 60-mM K+ solution. The [Mg2+]i increase was observed in the absence of extracellular Mg2+, but the increase disappeared in the absence of extracellular Ca2+. 50 microM cadmium or 100 microM verapamil, a Ca2+ channel blocker, also diminished the rise of [Mg2+]i. The additional measurement of an intracellular Ca2+ concentration ([Ca2+]i) indicated that the [Mg2+]i rise requires a threshold concentration of [Ca2+]i to be reached; above 60 nM. The present results indicate that depolarization induces a Ca2+-influx through voltage dependent Ca channels and this causes the release of Mg2+ from intracellular stores into the cytoplasm.