Effects of Apigenin on Glutamate-induced [Ca<SUP>2+</SUP>]<SUB>i</SUB> Increases in Cultured Rat Hippocampal Neurons

Effects of Apigenin on Glutamate-induced [Ca<SUP>2+</SUP>]<SUB>i</SUB> 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 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 (1&#1356;M to 100&#1356;M) for 5 min inhibited glutamate (100&#1356;M, 1 min) induced [Ca²⁺]_i increase, concentration-dependently. Pretreatment with apigenin (30&#1356;M) 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, 10&#1356;M, 1 min) and N-methyl-D-aspartate (NMDA, 100&#1356;M, 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 [Ca^₂₊]_i responses induced by the metabotropic glutamate receptor agonist, (S)-3,5-dihydroxy&lt;/SUB&gt;phenylglycine (DHPG, 100&#1356;M, 90 s), and inhibited the caffeine (10 mM, 2 min)-induced [Ca²⁺]_i responses. Furthermore, treatment with apigenin (30&#1356;M) significantly inhibited the amplitude and frequency of 0.1 mM [Mg^₂₊]_o-induced [Ca^₂₊]_i spikes. These data together suggest that apigenin inhibits glutamate-induced calcium signaling in cultured rat hippocampal neurons.