P2X receptors in peripheral neurons

P2X receptors are a family of ligand-gated ion channels, activated by extra cellular ATP. The seven subunits cloned (P2X,,) can assemble to form homome ric and heteromeric receptors. Peripheral neurons of neural crest origin (e .g. those in dorsal root, trigeminal, sympathetic and enteric ganglia) and placodal origin (e,g. those in nodose and petrosal ganglia) express mRNAs f or multiple P2X subunits. In this review, we summarize the molecular biolog ical, electrophysiological and immunohistochemical evidence for P2X recepto r subunits in sensory, sympathetic, parasympathetic, pelvic and myenteric n eurons and adrenomedullary chromaffin cells, We consider the pharmacologica l properties of these native P2X receptors and their physiological roles. T he responses of peripheral neurons to ATP show considerable heterogeneity b etween cells in the same ganglia, between ganglia and between species. Neve rtheless, these responses can all be accounted for by the presence of P2X(2 ) and P2X(3) subunits, giving rise to varying proportions of homomeric and heteromeric receptors. While dorsal root ganglion neurons express predomina ntly P2X, and rat sympathetic neurons express mainly P2X, receptors, nodose and guinea-pig sympathetic neurons express mixed populations of P2X(2) and heteromeric P2X(2.3) receptors, P2X receptors are important for synaptic t ransmission in enteric ganglia, although their roles in sympathetic and par asympathetic ganglia are less clear. Their presence on sensory neurons is e ssential for some processes including detection of filling of the urinary b ladder. The regulation of P2X receptor expression in development and in pat hological conditions. along with the interactions between purinergic and ot her signalling systems, may reveal further physiological roles for P2X rece ptors in autonomic and sensory ganglia. (C) 2001 Elsevier Science Ltd. All rights reserved.