We describe a new chicken P2X subunit that is an orthologue of the mammalian P2X 1 receptor. Functional characterization of chicken P2X 1 receptors was performed using the amphotericin B perforated patch configuration to avoid the current run-down observed under whole-cell patch-clamp conditions. Responses to agonists and to the antagonist PPADS (pyridoxal 5-phosphate 6-azophenyl-2',4'-disulfonic acid) were similar to what has been described for mammalian orthologues. However, the antagonists suramin and NF023 were much less potent at chicken P2X 1 receptors than at human P2X 1 receptors. In embryonic tissues, transcript expression is predominant in lung, liver and skeletal muscle. Overlapping expression with cP2X 4 and cP2X 5 subunits in several embryonic tissues, including skeletal muscle, indicates that the native embryonic P2X receptors could be heteromultimeric.