P-2X RECEPTORS BRING NEW STRUCTURE TO LIGAND-GATED ION CHANNELS

P-2X receptors are cation-selective ion channels that open on binding to extracellular ATP; they play a role in fast synaptic transmission between neurones, and from autonomic nerves to smooth muscles. Isolation of cDNAs that encode P-2X receptors in the smooth muscle of vas deferens and in phaeochromocytoma cells indicates that the receptors are not related to other ligand-gated ion channels. Their overall structure resembles more closely that of epithelial Na+ channels and the proteins that are thought to form mechanosensitive channels in Caenorhabditis elegans. The type of P-2X RNA that is found in vas deferens is expressed preferentially by apoptotic thymocytes, and the type of P-2X RNA that is found in PC12 cells is abundant in the pituitary gland, suggesting hitherto unsuspected roles for ATP-gated channels in endocrine and immune function.