Nucleotides, the structural subunits of the nucleic acids, are also important extracellular signaling molecules. P2 receptors are a family of cell surface receptors that mediate a wide variety of physiologic effects in response to extracellular nucleotides. These receptors fall into two classes: P2X receptors, which are ligand-gated ion channels that mediate calcium and potassium fluxes in response to ATP, and P2Y receptors, which are G protein-coupled receptors (GPCRs) (PMID: 21724990). P2RX7 functions as a ligand-gated ion channel and is responsible for ATP-dependent lysis of macrophages through the formation of membrane pores permeable to large molecules. P2RX7 is highly expressed by cells of the haemopoietic lineage and can mediate cell death, killing of infectious organisms, and regulation of the inflammatory response (PMID: 22102807).