6 Purinoceptors in the upper urinary tract

There is now abundant evidence for ATP acting as an extracellular signalling molecule. Receptors for ATP have been cloned and characterised, including seven P2X ionotropic and eight P2Y metabotropic receptor subtypes, as well as four subtypes of P1 receptors sensitive to adenosine, a breakdown product of ATP. P2 purinoceptor subtypes are expressed on ureteral smooth muscle, urothelium and blood vessels involved in fast signalling and probably also slower, trophic signalling during development and regeneration. ATP released from the urothelial Correspondence/Reprint request: Prof. Geoffrey Burnstock, Autonomic Neuroscience Centre, Royal Free and University College Medical School, Rowland Hill Street, London NW3 2PF, United Kingdom E-mail: [email protected] Geoffrey Burnstock 78 cells during distension of the ureter has been shown to act on P2X3 receptors expressed on suburothelial sensory nerves, sending nociceptive messages via dorsal root ganglia to pain centres in the central nervous system. P2X3 receptor antagonists are being explored for alleviating renal colic. ATP contracts while adenosine relaxes ureteric smooth muscle. P2X7 receptors have been implicated in macrophage infiltration, collagen deposition and apoptosis in response to ureteral obstruction in mice.