Flavonoids have been shown to affect calcium signaling in neurons. However, there are no reports on the effect of apigenin on glutamate-induced calcium signaling in neurons. We investigated whether apigenin affects glutamate-induced increase of free intracellular Ca2+ concentration ([Ca2+]i) in cultured rat hippocampal neurons, using fura-2-based digital calcium imaging and microfluorimetry. The hippocampal neurons were used between 10 and 13 days in culture from embryonic day 18 rats. Pretreatment of the cells with apigenin (1ՌM to 100ՌM) for 5 min inhibited glutamate (100ՌM, 1 min) induced [Ca2+]i increase, concentration-dependently. Pretreatment with apigenin (30ՌM) for 5 min significantly decreased the [Ca2+]i responses induced by two ionotropic glutamate receptor agonists, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPA, 10ՌM, 1 min) and N-methyl-D-aspartate (NMDA, 100ՌM, 1 min), and significantly inhibited the AMPA-induced peak currents. Treatment with apigenin also significantly inhibited the [Ca2+]i response induced by 50 mM KCl solution, decreased the [Ca2+]i responses induced by the metabotropic glutamate receptor agonist, (S)-3,5-dihydroxy</SUB>phenylglycine (DHPG, 100ՌM, 90 s), and inhibited the caffeine (10 mM, 2 min)-induced [Ca2+]i responses. Furthermore, treatment with apigenin (30ՌM) significantly inhibited the amplitude and frequency of 0.1 mM [Mg2+]o-induced [Ca2+]i spikes. These data together suggest that apigenin inhibits glutamate-induced calcium signaling in cultured rat hippocampal neurons.