Genomic structure, developmental distribution and functional properties of the chicken P2X₅ receptor

We report here the cloning of a chicken cDNA (402 aa) showing high sequence similarity to the previously cloned rat and human P2X₅ receptors (67 and 69%, respectively). The chicken P2X₅ subunit is encoded by a gene composed of 12 translated exons, which shows conserved genomic structure with mammalian P2X genes. In HEK-293 cells heterologously expressing chicken P2X₅ receptors, ATP activates a current that desensitizes in a way that is dependent on the presence of extracellular divalent cations. ATP and 2-methylthio ATP are equipotent agonists (EC₅₀ ∼ 2 μM) and suramin and pyridoxal 5-phosphate-6-azophenyl-2′,4′-disulfonic acid are potent antagonists. Additionally, reversal potential measurements indicate that chicken P2X₅ is permeable not only to cations but also to chloride (P_cs+/P_cl- ∼ 1.9), as has been described for native P2X receptor mediated responses in embryonic chicken skeletal muscle. mRNA distribution of chicken P2X₅ was determined by in situ hybridization analysis in both whole embryos and on tissue slices of heart and skeletal muscle. Our results suggest that chicken P2X₅ receptors are expressed in developing muscle and might play a rote in early muscle differentiation.