ATP is Required and Advances Cytokine-Induced Gap Junction Formation in Microglia In Vitro

Microglia are the immune cells in the central nervous system. After injury microglia release bioactive molecules, including cytokines and ATP, which modify the functional state of hemichannels (HCs) and gap junction channels (GJCs), affecting the intercellular communication via extracellular and intracellular compartments, respectively. Here, we studied the role of extracellular ATP and several cytokines as modulators of the functional state of microglial HCs and GJCs using dye uptake and dye coupling techniques, respectively. In microglia and the microglia cell line EOC20, ATP advanced the TNF-alpha/IFN-gamma-induced dye coupling, probably through the induction of IL-1 beta release. Moreover, TNF-alpha/IFN-gamma, but not TNF-alpha plus ATP, increased dye uptake in EOC20 cells. Blockade of Cx43 and Panx1 HCs prevented dye coupling induced by TNF-alpha/IFN-gamma, but not TNF-alpha plus ATP. In addition, IL-6 prevented the induction of dye coupling and HC activity induced by TNF-alpha/IFN-gamma in EOC20 cells. Our data support the notion that extracellular ATP affects the cellular communication between microglia through autocrine and paracrine mechanisms, which might affect the timing of immune response under neuroinflammatory conditions.