P2X5

P2X5 is a member of the P2X receptor family, a class of ATP-gated cation channels expressed by many cell types. The P2X receptors are trimeric channels formed from three subunits; each subunit has two membrane-spanning domains with a large extracellular domain that binds ATP. When extracellular ATP binds at the interface between subunits, the channel opens and allows cations, notably Na+ and Ca2+, to enter the cell, contributing to depolarization and intracellular signaling.

In humans, the P2RX5 gene is considered a pseudogene because the canonical transcript contains a premature stop codon, and no functional P2X5 protein is produced. Consequently, there is limited evidence for P2X5-mediated signaling in human tissues. In many non-human vertebrates, functional P2X5 proteins are expressed and can form homomeric channels or heteromerize with other P2X subunits, with tissue distributions reported in the nervous system, immune tissues, and sensory organs in different species. The exact physiological roles of P2X5 vary and are still being studied, but P2X5 is implicated in processes such as synaptic transmission, nociception, and inflammatory signaling where P2X receptors contribute.

Pharmacology of P2X5 is less characterized than that of more ubiquitously expressed subunits like P2X3 or P2X4; ATP is the primary activator, and receptor responses can be modulated by extracellular divalent cations and pharmacological agents in research settings. Because humans generally lack functional P2X5, its relevance to human physiology and disease remains uncertain and is mainly of interest in comparative and evolutionary studies of the P2X receptor family. See also: P2X receptor, purinergic signaling.