The P2X receptors belong to the ligand-gated ion channel family and are activated by extracellular ATP. The structure and function of the P2X receptors, investigated mainly using in vitro models, indicate their involvement in synaptic communication, cell death, and differentiation. Seven mammalian P2X receptor subtypes (P2X1–P2X7) have been identified and cloned. All P2X receptor subtypes share the same structure of intracellular N and C-termini two membrane-spanning domains and a large extracellular loop.