P2X 1 and P2X 4 receptor currents in mouse macrophages

Background and purpose: Activation of P2X receptors on macrophages is an important stimulus for cytokine release. This study seeks evidence for functional expression of P2X receptors in macrophages that had been only minimally activated. Experimental approach: Whole-cell recordings were made from macrophages isolated 2-6 h before by lavage from mouse peritoneum, without further experimental activation. ATP (1-1000 μM) elicited inward currents in all cells (holding potential -60 mV). The properties of this current were compared among cells from wild type, P2X 1 -/- and P2X 4 -/- mice. Key results: Immunoreactivity for P2X 1 and P2X 4 receptors was observed in wild type macrophages but was absent from the respective knock-out mice. In cells from wild type mice, ATP and αβmethyleneATP (αβmeATP) evoked inward currents rising in 10-30 ms and declining in 100-300 ms: these were blocked by pyridoxal-phosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS, 10 μM). ATP also elicited a second, smaller (∼10% peak amplitude), more slowly decaying (1-3 s) at concentrations ≥10 μM: this was resistant to PPADS and prolonged by ivermectin. Macrophages from P2X 1 -/- mice responded to ATP (≥100 μM) but not αβmeATP: these small currents were prolonged by ivermectin. Macrophages from P2X 4 -/- mice responded to ATP and αβmeATP as cells from wild type mice, except that ATP did not evoke the small, slowly decaying component: these currents were blocked by PPADS. Conclusion: Mouse peritoneal macrophages that are minimally activated demonstrate membrane currents in response to ATP and αβmeATP that have the predominate features of P2X 1 receptors. © 2007 Nature Publishing Group All rights reserved.