Calcium dynamics in neurons treated with toxic and non-toxic concentrations of glutamate

Abstract

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 μM GLU caused an initial transient increase in [Ca²⁺]ⁱ; 20 μM a biphasic response characterized by a 150–350 s 'calcium trough' between peaks; and 40 μM an initial sustained increase in [Ca²⁺]ⁱ. Neurons in calcium-free medium treated with 40 μM 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.