Octyl Gallate Inhibits ATP-induced Intracellular Calcium Increase in PC12 Cells by Inhibiting Multiple Pathways

Octyl Gallate Inhibits ATP-induced Intracellular Calcium Increase in PC12 Cells by Inhibiting Multiple Pathways

Phenolic compounds affect intracellular free Ca^2＋ concentration ([Ca^2＋]_i) signaling. The study examined whether the simple phenolic compound octyl gallate affects ATP-induced Ca^2＋ signaling in PC12 cells using fura-2-based digital Ca^2＋ imaging and whole-cell patch clamping. Treatment with ATP (100</SUP>ՌM) for 90 s induced increases in [Ca^2＋]_i in PC12 cells. Pretreatment with octyl gallate (100 nM to 20ՌM) for 10 min inhibited the ATP-induced [Ca^2＋]_i response in a concentration-dependent manner (IC₅₀=2.84ՌM). Treatment with octyl gallate (3ՌM) for 10 min significantly inhibited the ATP-induced response following the removal of extracellular Ca^2＋ with nominally Ca^2＋-free HEPES HBSS or depletion of intracellular Ca^2＋ stores with thapsigargin (1ՌM). Treatment for 10 min with the L-type Ca^2＋ channel antagonist nimodipine (1ՌM) significantly inhibited the ATP-induced [Ca^2＋]_i increase, and treatment with octyl gallate further inhibited the ATP-induced response. Treatment with octyl gallate significantly inhibited the [Ca^2＋]_i increase induced by 50 mM KCl. Pretreatment with protein kinase C inhibitors staurosporin (100 nM) and GF109203X (300 nM), or the tyrosine kinase inhibitor genistein (50ՌM) did not significantly affect the inhibitory effects of octyl gallate on the ATP-induced response. Treatment with octyl gallate markedly inhibited the ATP-induced currents. Therefore, we conclude that octyl gallate inhibits ATP-induced [Ca^2＋]_i increase in PC12 cells by inhibiting both non-selective P2X receptor-mediated influx of Ca^2＋ from extracellular space and P2Y receptor-induced release of Ca^2＋ from intracellular stores in protein kinase-independent manner. In addition, octyl gallate inhibits the ATP-induced Ca^2＋ responses by inhibiting the secondary activation of voltage-gated Ca^2＋ channels.