P2X receptors are trimeric proteins formed by subunits with two transmembrane domains. There are at least seven subtypes of P2X receptors ranging from P2X1 to P2X7. Immunohistochemical studies using specific P2X receptor antibodies found at least three P2X receptor subunits in the ENS that were identified as P2X2, P2X3, and P2X7. The P2X2 receptor is expressed in neurons that express immunoreactivity for the chemical codes of inhibitory musculomotor neurons, non-cholinergic secretomotor neurons, and calbindin-immunoreactive neurons.200 Loss of the purinergic component of fast EPSPs in P2X2 knockout mice supports the suggestion that the P2X2 receptor is a major player in purinergic fast transmission in enteric neurons. P2X3-subunits form heteromers with P2X2-subunits in aborally projecting inhibitory musculomotor neurons. Calbindin-immunoreactive enteric neurons do not express P2X3 receptor immunoreactivity.