Abstract
Alveolar macrophages (AM) are crucial for pulmonary host defense, and evidence emerges that ATP-gated P2X receptors are involved in inflammatory processes. This study focuses on the expression and functional characterization of P2X receptors in AM from mouse. In RT-PCR experiments, transcripts encoding the P2X(1), P2X(3), P2X(4), P2X(5), and P2X(7) receptors were detected. In whole-cell patch-clamp recordings, ATP (1 mM) evoked an inward current (mouse and human AM) that was reversible upon washout, and the reversal potential was similar to 5 mV, indicating the activation of a non-selective conductance-a fingerprint of P2X receptors. Further characterization (mouse AM) revealed that the current was not desensitized by a second ATP application. The ATP-induced current was increased by the removal of extracellular Ca2+ (in human and mouse AM), and EC50 in mouse AM were determined with similar to 1 mM ATP, in the presence as well as in the absence of extracellular Ca2+. Pharmacological characterization of mouse AM revealed that the effect was augmented by BzATP and pre-application with ivermectin, but no effect with alpha,beta-meATP was observed. Further, the ATP effect was reduced by PPADS (300 mu M), brilliant blue G (5 mu M), and about A438079 (10 mu M). Although different P2X receptor transcripts were detected in mouse AM, the observed functional and pharmacological characteristics indicate primarily the participation of P2X(4) and P2X(7) receptors as mediators of the ATP-induced ion current in mouse AM. These suggestions were confirmed by experiments with AM from P2X(7)-deficient animals, indicating a contribution of P2X(4) and P2X(7) receptors in pulmonary immune function.