ATP stimulation of P2X(7) receptors activates three different ionic conductances on cultured mouse Schwann cells

Extracellular ATP, by acting on P2 purinergic receptors, is a potent mediat or of cell-to-cell communication both within and between the nervous and th e immune systems. We show here by patch-clamp recording, fluorescent dye up take and immunocytochemistry that, in cultured mouse Schwann cells, ATP act ivates a P2X(7) receptor associated with three different ionic conductances . In control conditions, ATP activated an inward current (I-ATP) with a low potency (EC50, 7.2 mM). Replacing ATP either by the ATP analogue 2',3'-O-( 4-benzoyl-4-benzoyl)-ATP (BzATP) or by the tetraacidic form ATP(4-) potenti ated the inward current (ATP(4-) EC50, 375 muM). ATP and BzATP currents wer e strongly reduced by periodate oxidized ATP (oATP), an antagonist of P2X(7 ) receptors. I-ATP was a mixed current composed of a nonselective cationic conductance, a cationic conductance selective for K+ and an anionic conduct ance selective for Cl-. The activation of the K+ conductance was dependent on an influx of Ca2+, and was blocked by charybdotoxin (ChTX) and tetraethy lammonium (TEA), two potent antagonists of large conductance Ca2+- activate d K+ channels (BK channels). The activation of the Cl- conductance was inse nsitive to Ca2+ but required the presence of K+. Total removal of K+ blocke d both the Ca2+-activated K+ conductance and the Cl- conductance, unveiling the P2X(7) nonselective cationic conductance. The P2X(7) receptor was loca lized by immunocytochemistry using a polyclonal antibody, anti-P2X(7), whil st its expression and functionality were both detected by the uptake of Luc ifer Yellow. This receptor could regulate the synthesis and the release of cytokines by Schwann cells during pathophysiological events.