Bradykinin-induced Ca(2+) signaling in human subcutaneous fibroblasts involves ATP release via hemichannels leading to P2Y(12) receptors activation

BACKGROUND: Chronic musculoskeletal pain involves connective tissue remodeling triggered by inflammatory mediators, such as bradykinin. Fibroblast cells signaling involve changes in intracellular Ca(2+) ([Ca(2+)](i)). ATP has been related to connective tissue mechanotransduction, remodeling and chronic inflammatory pain, via P2 purinoceptors activation. Here, we investigated the involvement of ATP in bradykinin-induced Ca(2+) signals in human subcutaneous fibroblasts. RESULTS: Bradykinin, via B(2) receptors, caused an abrupt rise in [Ca(2+)](i) to a peak that declined to a plateau, which concentration remained constant until washout. The plateau phase was absent in Ca(2+)-free medium; [Ca(2+)](i) signal was substantially reduced after depleting intracellular Ca(2+) stores with thapsigargin. Extracellular ATP inactivation with apyrase decreased the [Ca(2+)](i) plateau. Human subcutaneous fibroblasts respond to bradykinin by releasing ATP via connexin and pannexin hemichannels, since blockade of connexins, with 2-octanol or carbenoxolone, and pannexin-1, with (10)Panx, attenuated bradykinin-induced [Ca(2+)](i) plateau, whereas inhibitors of vesicular exocytosis, such as brefeldin A and bafilomycin A1, were inactive. The kinetics of extracellular ATP catabolism favors ADP accumulation in human fibroblast cultures. Inhibition of ectonucleotidase activity and, thus, ADP formation from released ATP with POM-1 or by Mg(2+) removal from media reduced bradykinin-induced [Ca(2+)](i) plateau. Selective blockade of the ADP-sensitive P2Y(12) receptor with AR-C66096 attenuated bradykinin [Ca(2+)](i) plateau, whereas the P2Y(1) and P2Y(13) receptor antagonists, respectively MRS 2179 and MRS 2211, were inactive. Human fibroblasts exhibited immunoreactivity against connexin-43, pannexin-1 and P2Y(12) receptor. CONCLUSIONS: Bradykinin induces ATP release from human subcutaneous fibroblasts via connexin and pannexin-1-containing hemichannels leading to [Ca(2+)](i) mobilization through the cooperation of B(2) and P2Y(12) receptors.