Inhibition of Mg(2+) Extrusion Attenuates Glutamate Excitotoxicity in Cultured Rat Hippocampal Neurons

Magnesium plays important roles in the nervous system. An increase in the Mg(2+) concentration in cerebrospinal fluid enhances neural functions, while Mg(2+) deficiency is implicated in neuronal diseases in the central nervous system. We have previously demonstrated that high concentrations of glutamate induce excitotoxicity and elicit a transient increase in the intracellular concentration of Mg(2+) due to the release of Mg(2+) from mitochondria, followed by a decrease to below steady-state levels. Since Mg(2+) deficiency is involved in neuronal diseases, this decrease presumably affects neuronal survival under excitotoxic conditions. However, the mechanism of the Mg(2+) decrease and its effect on the excitotoxicity process have not been elucidated. In this study, we demonstrated that inhibitors of Mg(2+) extrusion, quinidine and amiloride, attenuated glutamate excitotoxicity in cultured rat hippocampal neurons. A toxic concentration of glutamate induced both Mg(2+) release from mitochondria and Mg(2+) extrusion from cytosol, and both quinidine and amiloride suppressed only the extrusion. This resulted in the maintenance of a higher Mg(2+) concentration in the cytosol than under steady-state conditions during the ten-minute exposure to glutamate. These inhibitors also attenuated the glutamate-induced depression of cellular energy metabolism. Our data indicate the importance of Mg(2+) regulation in neuronal survival under excitotoxicity.