Genomic structure, developmental distribution and functional properties ofthe chicken P2X(5) receptor

We report here the cloning of a chicken cDNA (402 aa) showing high sequence similarity to the previously cloned rat and human P2X(5) receptors (67 and 69%, respectively). The chicken P2X(5) subunit is encoded by a gene compos ed of 12 translated exons, which shows conserved genomic structure with mam malian P2X genes. In HEK-293 cells heterologously expressing chicken P2X(5) receptors, ATP activates a current that desensitizes in a way that is depe ndent on the presence of extracellular divalent cations. ATP and 2-methylth io ATP are equipotent agonists (EC50 similar to 2 muM) and suramin and pyri doxal 5-phosphate-6-azophenyl-2 ' ,4 ' -disulfonic acid are potent antagoni sts. Additionally, reversal potential measurements indicate that chicken P2 XS is permeable not only to cations but also to chloride (PCs+/PCl- similar to 1.9), as has been described for native P2X receptor mediated responses in embryonic chicken skeletal muscle. mRNA distribution of chicken P2X(5) w as determined by in situ hybridization analysis in both whole embryos and o n tissue slices of heart and skeletal muscle. Our results suggest that chic ken P2X(5) receptors are expressed in developing muscle and might play a ro le in early muscle differentiation.