Effects of Apigenin on Glutamate-induced [Ca](i) Increases in Cultured Rat Hippocampal Neurons.

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 Ca(2+) concentration (Ca(2+)) 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 (1 microM to 100 microM) for 5 min inhibited glutamate (100 microM, 1 min) induced Ca(2+) increase, concentration-dependently. Pretreatment with apigenin (30 microM) for 5 min significantly decreased the Ca(2+) responses induced by two ionotropic glutamate receptor agonists, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPA, 10 microM, 1 min) and N-methyl-D-aspartate (NMDA, 100 microM, 1 min), and significantly inhibited the AMPA-induced peak currents. Treatment with apigenin also significantly inhibited the Ca(2+) response induced by 50 mM KCl solution, decreased the Ca(2+) responses induced by the metabotropic glutamate receptor agonist, (S)-3,5-dihydroxyphenylglycine (DHPG, 100 microM, 90 s), and inhibited the caffeine (10 mM, 2 min)-induced Ca(2+) responses. Furthermore, treatment with apigenin (30 microM) significantly inhibited the amplitude and frequency of 0.1 mM Mg(2+)-induced Ca(2+) spikes. These data together suggest that apigenin inhibits glutamate-induced calcium signaling in cultured rat hippocampal neurons.