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 b etween neurones, and from autonomic nerves to smooth muscles. Isolatio n of cDNAs that encode P-2X receptors in the smooth muscle of vas defe rens and in phaeochromocytoma cells indicates that the receptors are n ot related to other ligand-gated ion channels. Their overall structure resembles more closely that of epithelial Na+ channels and the protei ns that are thought to form mechanosensitive channels in Caenorhabditi s elegans. The type of P-2X RNA that is found in vas deferens is expre ssed preferentially by apoptotic thymocytes, and the type of P-2X RNA that is found in PC12 cells is abundant in the pituitary gland, sugges ting hitherto unsuspected roles for ATP-gated channels in endocrine an d immune function.