P2X currents in peritoneal macrophages of wild type and P2X4−/− mice

In this study the ATP-induced (P2X) currents in isolated peritoneal macrophages of wild type (WT) and P2X4 knockout (P2X4−/−) mice were studied by means of whole-cell patch clamp in order to (1) survey the P2X currents of native macrophages and (2) to investigate the expression of P2X4-like currents in the WT versus P2X4−/− mice. Three types of currents were observed in the isolated macrophages: (1) in ∼10% of both WT and P2X4−/− macrophages a fast activating and inactivating P2X1-like current was recorded with low concentrations (0.1–1 μM) of ATP; (2) 85% of wild type and 100% of P2X4−/− macrophages exhibited a non-desensitizing P2X7-like current activated at high concentrations of ATP (10 mM). The identity of the P2X7 current was confirmed using the specific blocker A-740003; (3) 88.6% of the WT but none of the P2X4−/− macrophages showed a small P2X4-like current that desensitized slowly upon ATP application at intermediate concentrations (3–300 μM). Several observations indicated that the slowly desensitizing current in WT macrophages was P2X4. The EC50 value of 5.3 μM ATP was as expected for P2X4 and the current induced by 3–300 μM ATP was absent in P2X4−/− mice. Upon application of 3 μM ivermectin, a P2X4-selective modulator, the amplitude of this current was increased and the desensitization was inhibited in WT cells. In addition, this current was facilitated by 10 μM Zn2+ but inhibited by Cu2+ (in contrast to P2X2). We conclude that the P2X4 and P2X7 currents are functionally expressed in recruited peritoneal macrophages of WT mice and that the P2X4-like current is absent in P2X4−/− mice.