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 S-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 mu M cadmium or 100 mu M 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. (C) 1998 Elsevier Science B.V.