To characterize the regulatory mechanism of phospholipase C-delta 1 (PLC-delta 1) in the bradykinin (BK) receptor-mediated signaling pathway, we used a clone of PC12 cells, which stably overexpress PLC-delta 1 (PC12-D1). Stimulation with BK induced a significantly higher Ca2+ elevation and inositol 1,4,5-trisphosphate (IP3) production with a much lower half-maximal effective concentration (EC50) of BK in PC12-D1 cells than in wild type (PC12-W) or vector-transfected (PC12-V) cells. However, BK-induced intracellular Ca2+ release and IF, generation was similar between PC12-V and PC12-D1 cells in the absence of extracellular Ca2+, suggesting that the availability of extracellular Ca2+ is essential to the activation of PLC-delta 1. When PC12-D1 cells were treated with agents that induce Ca2+ influx, more IP3 was produced, suggesting that the Ca2+ entry induces IP3 production in PC12-D1 cells. Furthermore, the additional IP3 production after BK-induced capacitative calcium entry was detected in PC12-D1 cells, suggesting that PLC-delta 1 is mainly activated by capacitative calcium entry. When cells were stimulated with BK in the presence of extracellular Ca2+, [H-3]norepinephrine secretion was much greater from PC12-D1 cells than from PC12-V cells. Our results suggest that PLC-delta 1 is activated by capacitative calcium entry following the activation of PLC-P, additively inducing IF, production and Ca2+ rise in BK-stimulated PC12 cells.
