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, which were mainly investigated 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.^1,2,3 All P2X receptor subtypes share the same structure of intracellular N- and C-termini, two membrane-spanning domains and a large extracellular loop. All P2X subtypes can assemble to form homomeric or heteromeric functional channels with the exception of P2X6, which only seems to function as part of a heteromeric complex.^4-9

The various mammalian P2X receptors show distinct expression patterns. P2X1-6 have been found in the central and peripheral nervous system, while the P2X7 receptor is predominantly found in cells of the immune system.⁴ The P2X2 receptor subtypes has a widespread tissue distribution in autonomic neurons, but it is generally found to be co-expressed with one or more subtypes.

mRNA of the P2X1, P2X2, P2X3, and P2X6 receptors is found in neurons of dorsal root ganglia (DRG), trigeminal, and nodose ganglia where heteromeric P2X2/P2X3 receptors are found.¹⁰