Subcellular localization of glutamate-stimulated intracellular magnesium concentration changes in cultured rat forebrain neurons using confocal microscopy.
Glutamate can stimulate increases in intracellular magnesium concentration ([Mg2+]i) and induce neurotoxicity, both independent of Ca2+ changes. Although Mg2+ is essential within the cell, very little is known about how it is regulated, especially in neurons. Therefore we used the fluorescent indicator, magindo-1 and confocal microscopy to examine possible intracellular pools of Mg2+ in cultured neurons that can be dynamically regulated by glutamate. The magindo-1 fluorescence signal was present throughout the cell body and extends into the neuronal processes. The magindo-1 405 nm/490 nm ratio signal was similar in the cytoplasm and nucleus, suggesting that resting [Mg2+]i is uniform across the neuron. The addition of 100 microM glutamate/10 microM glycine in an extracellular Ca2+- and Na+-free buffer stimulated an increase in [Mg2+]i in both the nuclear and cytoplasmic regions of similar magnitude and duration. This glutamate exposure also stimulated a [Mg2+]i increase in neuronal processes which was inhibited by the N-methyl-D-aspartate receptor antagonist, MK-801 (10 microM). The glutamate-stimulated [Mg2+]i increase in both the cell body and neuronal processes was dependent on the extracellular Mg2+ concentration. These findings suggest glutamate-stimulated [Mg2+]i changes may not only impact cytoplasmic processes, but also directly trigger nuclear events involved, for example, in neuronal injury.