GLUTAMATE-INDUCED INCREASES IN INTRACELLULAR FREE MG(2-NEURONS() IN CULTURED CORTICAL)

Intracellular free Mg2+ concentrations ([Mg2+]i) in single rat brain n eurons were measured with the Mg2+-sensitive fluorescent dye magfura-2 . Addition of glutamate with glycine raised [Mg2+]i from 1 to more tha n 11 mM compared with the resting concentration of 0.5 mM, an effect m ediated by N-methyl-D-aspartate receptors. Most of the increase in [Mg 2+]i was independent of extracellular Mg2+, but was dependent on extra cellular Ca2+. The second component of the increase induced by glutama te was independent of extracellular Ca2+, but required extracellular M g2+ and was amplified by extracellular Na+ removal. These results indi cate that regulation of [Mg2+]i by neurotransmitters such as glutamate may be important in controlling neuronal excitability.