The ATP-gated P2X Receptor Cation Channel (P2X Receptor) Family (TC# 1.A.7) consists of cation-permeable ligand gated ion channels that open in response to the binding of extracellular adenosine 5'-triphosphate (ATP). They belong to a larger family of receptors known as the ENaC/P2X superfamily.^[14] ENaC and P2X receptors have similar 3-D structures and are homologous.^[15] P2X receptors are present in a diverse array of organisms including humans, mouse, rat, rabbit, chicken, zebrafish, bullfrog, fluke, and amoeba.

P2X receptors are involved in a variety of physiological processes, including:

P2X receptors are expressed in cells from a wide variety of animal tissues. On presynaptic and postsynaptic nerve terminals and glial cells throughout the central, peripheral and autonomic nervous systems, P2X receptors have been shown to modulate synaptic transmission. Furthermore, P2X receptors are able to initiate contraction in cells of the heart muscle, skeletal muscle, and various smooth muscle tissues, including that of the vasculature, vas deferens and urinary bladder. P2X receptors are also expressed on leukocytes, including lymphocytes and macrophages, and are present on blood platelets. There is some degree of subtype specificity as to which P2X receptor subtypes are expressed on specific cell types, with P2X₁ receptors being particularly prominent in smooth muscle cells, and P2X₂ being widespread throughout the autonomic nervous system. However, such trends are very general and there is considerable overlap in subunit distribution, with most cell types expressing more than one subunits. For example, P2X₂ and P2X₃ subunits are commonly found co-expressed in sensory neurons, where they often co-assemble into functional P2X_2/3 receptors.

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