Endoplasmic Reticulum Is a Key Organella in Bradykinin-Triggered ATP Release From Cultured Smooth Muscle Cells

Abstract

ATP has broad functions as an autocrine/paracrine molecule. The mode of ATP release and its intracellular source, however, are little understood. Here we show that bradykinin via B₂-receptor stimulation induces the extracellular release of ATP via the inositol 1,4,5-trisphosphate [Ins(1,4,5)P₃]-signaling pathway in cultured taenia coli smooth muscle cells. It was found that bradykinin also increased the production of Ins(1,4,5)P₃ and 2-APB-inhibitable [Ca²⁺]_i. The evoked release of ATP was suppressed by the Ca²⁺-channel blockers, nifedipine, and verapamil. Moreover, the extracellular release of ATP was elicited by photoliberation of Ins(1,4,5)P₃. Bradykinin caused a quick and transient accumulation of intracellular ATP from cells treated with 1% perchloric acid solution (PCA), but not with the cell lysis buffer. Peak accumulation was prevented by 2-APB and thapsigargin, but not by nifedipine or verapamil, inhibitors of extracellular release of ATP. These findings suggest that bradykinin elicits the extracellular release of ATP that is mediated by the Ins(1,4,5)P₃-induced Ca²⁺ signaling and, finally, leads to a Ca²⁺-dependent export of ATP from the cells. Furthermore, the bradykinin-induced transient accumulation of ATP in the cells treated with PCA may imply a possible release of ATP from the endoplasmic reticulum.