P2X₃ receptors and peripheral pain mechanisms

Abstract

ATP released from damaged or inflamed tissues can act at P2X receptors expressed on primary afferent neurones. The resulting depolarization can initiate action potentials that are interpreted centrally as pain. P2X 3 subunits are found in a subset of small-diameter, primary afferent neurones, some of which are also sensitive to capsaicin. They can form homo-oligomeric channels, or they can assemble with P2X 2 subunits into hetero-oligomers. Studies with antagonists selective for P2X 3 -containing receptors, experiments with antisense oligonucleotides to reduce P2X 3 subunit levels, and behavioural testing of P2X 3 knock-out mice, all suggest a role for the P2X 2/3 receptor in the signalling of chronic inflammatory pain and some features of neuropathic pain. The availability of such tools and experimental approaches promises to accelerate our understanding of the other physiological roles for P2X receptors on primary afferent neurones.

Distribution of purinergic P2X receptors in the equine digit, cervical spinal cord and dorsal root ganglia

“…Protein samples (25 μg) were mixed with lane marker non-reducing sample buffer (ThermoScientific) and DTT (0.1 M) and denatured at 70°C for 10 min. Samples used in Western blots for P2X 1,[3][4][5][6][7] proteins were denatured, whereas samples for P2X 2 protein did not undergo denaturation since P2X 2 antibody showed better results with non-denatured samples. Samples and molecular weight markers were loaded and separated on NuPage 4-12 % Bis-Tris gel (Invitrogen) and then transferred onto nitrocellulose membrane (Whatman).…”

“…Subsequent to this analysis of P2X antibody binding specificity, the antibody sera for P2X 1-3 and P2X 7 were used for immunohistochemical analysis.…”

“…Tissue samples for immunohistochemical analysis of P2X [1][2][3]7 were fixed overnight in 4 % buffered PFA, paraffin embedded then cut in 6-μm sections. Sections were deparaffinised and rehydrated before being subjected to antigen retrieval …”

“…Since this time, ATP activation of purinergic signalling pathways has been described in neurons and related cells in both the peripheral and central nervous systems [2,7]. In addition to functions in the nervous tissues, the role of P2X receptor activation by ATP in non-excitable cells (such as leukocytes and epithelial cells) is being increasingly recognised [8].…”

“…mRNA signal for most of the tested P2X receptor subunits (P2X 1-5, 7 ) was detected in all sampled equine tissues, whereas P2X 6 receptor subunit was predominantly expressed in the dorsal root ganglia and spinal cord. Western blot analysis validated the specificity of P2X [1][2][3]7 antibodies, and these were used in immunohistochemistry studies. P2X 1-3, 7 receptor subunits were found in smooth muscle cells in the palmar digital artery and vein with the exception of the P2X 3 subunit that was present only in the vein.…”