Abstract
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 microM) for 90 s induced increases in [Ca(2+)](i) in PC12 cells. Pretreatment with octyl gallate (100 nM to 20 microM) for 10 min inhibited the ATP-induced [Ca(2+)](i) response in a concentration-dependent manner (IC(50)=2.84 microM). Treatment with octyl gallate (3 microM) 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 (1 microM). Treatment for 10 min with the L-type Ca(2+) channel antagonist nimodipine (1 microM) 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 (50 microM) 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.