CALCIUM DYNAMICS IN NEURONS TREATED WITH TOXIC AND NONTOXIC CONCENTRATIONS OF GLUTAMATE

INTRACELLULAR calcium concentration ([Ca2+]i) dynamics were simultaneously monitored in multiple cultured rat neurons loaded with Fluo-3 and continuously stimulated with glutamate (GLU). Three response types were observed: 10 muM GLU caused an initial transient increase in [Ca2+]i; 20 muM a biphasic response characterized by a 150-350 s 'calcium trough' between peaks; and 40 muM an initial sustained increase in [Ca2+]i. Neurons in calcium-free medium treated with 40 muM GLU showed only an initial transient increase in [Ca2+]i, demonstrating the dependence of sustained secondary increases in [Ca2+]i on extracellular calcium sources. We observed synchronized responses of multiple neurons within a given culture well, after GLU treatment, supporting the hypothesis that sustained influx of extracellular calcium may be stimulated by depletion of intracellular calcium and/or the release of endogenous excitatory amino acids.