Molecular characterization and pharmacological properties of the human P2X3 purinoceptor

Using PCR and library screening techniques, a cDNA encoding an ATP ligand-gated channel has been isolated from human heart. The full-length cDNA encodes a protein 397 amino acids long which shows a high amino-acid sequence identity with the rat P2X3 purinoceptor (93%). By fluorescence in situ hybridization, the human P2X3 gene has been mapped to region q12 of chromosome 11. Tissue distribution analysis of human P2X3 receptor mRNA shows a restricted expression pattern, i.e. transcripts are limited to the spinal cord and heart. This result contrasts with the distribution of the rat P2X3 receptor which was detected exclusively in sensory neurons of trigeminal, dorsal root and nodose ganglia. Heterologous expression of human P2X3 cRNA in Xenopus oocytes generates a fast desensitizing ATP-activated channel with pharmacological properties resembling the profile of the rat homologue receptor. Thus, the order of agonist potency is 2MeSATP > ATP > alphabeta-meATP > CTP > betagamma-meATP approximately ADP. Moreover, ATP-evoked currents on human P2X3 receptor are efficiently blocked in a reversible manner by the purinoceptor antagonists, suramin and PPADS.