Green tea has been receiving considerable attention as a possible neuroprotective agent against neurodegenerative disease. Epigallocatechin-3-gallate (EGCG) is the major compound of green tea. Calcium signaling has profound effects on almost all aspects of neuronal function. Using digital calcium imaging and patch-clamp technique, we determined the effects of EGCG on Ca(2+) signals in hippocampal neurons. The results indicated that EGCG caused a dose-dependent increase in intracellular Ca(2+) ([Ca(2+)](i)). This [Ca(2+)](i) increase was blocked by depleting intracellular Ca(2+) stores with the endoplasmic reticulum Ca(2+) pump inhibitor thapsigargin and cyclopiazonic acid. Furthermore, EGCG-stimulated increase in [Ca(2+)](i) was abolished following treatment with a PLC inhibitor. However, EGCG inhibited high-voltage activated Ca(2+) currents (I(HVA)) and NMDA-induced inward currents (I(NMDA)). These data suggest that EGCG triggers a cascade of events: it activates phospholipase C (PLC), mobilizes intracellular Ca(2+) stores, raises the cytosolic Ca(2+) levels, and inhibits the VGCC and NMDA receptors-mediated Ca(2+) influx through a process that remains to be determined.
Keywords: EGCG; calcium imaging; hippocampal neuron; intracellular Ca2+; phopholipase C.