Extrazellular ATP plays an important role as a signalling molecule in the innate immune response since it stimulates the release of pro-inflammatory mediators from macrophages. ATP binds to purinergic receptors which can be divided into G-protein-coupled receptors (P2Y) and ligand-gated ion channels (P2X). Although different types of purinergic receptors were identified in macrophages, there is only poor knowledge about the precise puringeric receptor repertoire and precise puringeric signalling mechanisms in alveolar macrophages. In our present study we focused on the role of ATP on ion transport processes in alveolar macrophages and the identification of the involved purinergic receptors. In whole-cell patch clamp recordings from either freshly isolated mouse alveolar macrophages or the cell-line NR8383, the application of ATP leds to a significant stimulation of the transmembrane current. This current was Ca²⁺ sensitive, since the effect was increased by Ca²⁺-free conditions. The removal of divalent cations like Ca²⁺ is known to augment the effect of ATP on the receptor subtype P2X₇. Therefore we questioned whether this receptor subtype was expressed in alveolar macrophages. RT-PCR revealed the presence of mRNA for P2X₅ and P2X₇ receptors.

We hypothesize that the the P2X₇ receptor plays an important role in purinergic signalling pathways in alveolar macrophages. The involvement of the P2X₇ receptor in purinergic pathways in alveoalar macrophages is not sudden, since the receptor is important for the realase of pro-inflammatory cytokines like IL-8 or IL-1ß.