Millimolar concentrations of free magnesium enhance exocytosis from permeabilized rat pheochromocytoma (PC 12) cells

The role of Mg2+ during the final steps of exocytosis was
investigated using rat pheochromocytoma cells (PC12) permeabilized
with bacterial pore forming toxins. Concentrations of free Mg2+
between 0.2 and 2 mM slightly lowered the basal but greatly
enhanced the [3H]dopamine release elicited by 8 μM free Ca2+.
Maximal effects were obtained at approximately 1 mM free Mg2+. At
higher concentrations Mg2+ was less potent. Similar effects of Mg2+
were obtained in cells permeabilized either for small molecules (by
α-toxin) or for large ones (by streptolysin O). It is concluded
that millimolar concentrations of cytoplasmic Mg2+ play an
important role in Ca2+ triggered exocytosis.