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P2X receptors are a subclass of ionotropic purinoceptors, which are ligand-gated ion channels activated by extracellular nucleotides, primarily adenosine triphosphate (ATP). These receptors are named for their sensitivity to purines, particularly ATP, and are categorized into P2X and P2Y subtypes based on their structural and functional differences. The P2X receptor family consists of seven distinct subunits, labeled P2X1 through P2X7, each encoded by separate genes.

P2X subunits assemble as trimers to form functional ion channels, allowing the influx of cations (primarily sodium and calcium) and the efflux of potassium when activated by ATP. This ion flux contributes to cellular excitability, neurotransmitter release, and inflammatory responses. The subunit composition of P2X receptors influences their pharmacological properties, localization, and physiological roles. For example, P2X1, P2X2, and P2X3 subunits often form heteromeric channels, while P2X7 tends to form homomeric channels with unique properties, such as large pore formation and activation of inflammatory signaling pathways.

P2X receptors are widely expressed across various tissues, including the central and peripheral nervous systems, immune cells, and vascular smooth muscle. In the nervous system, they play roles in synaptic transmission, pain perception, and neuroinflammation. Dysregulation of P2X receptor function has been implicated in several pathological conditions, including neurodegenerative diseases, chronic pain syndromes, and autoimmune disorders. Research into P2X receptors has also highlighted their potential as therapeutic targets for conditions such as ischemia, inflammation, and cancer.

The study of P2X subunits involves molecular biology, electrophysiology, and pharmacology to elucidate their structure-function relationships and physiological significance. Advances in these areas continue to expand understanding of how P2X receptors contribute to cellular signaling and disease mechanisms.