ATP-sensitive isoforms of P2X5: A reevaluation of its function across species

The P2X receptor family comprises ATP-gated non-selective cation channels central to physiological processes across the nervous, immune, cardiovascular, respiratory, and reproductive systems. While P2X1, P2X2, P2X3, P2X4, and P2X7 are well-established as ATP-sensitive, P2X5 isoforms and transcript variants (TVs) have traditionally been considered ATP-insensitive, limiting their functional exploration. This study identifies previously overlooked ATP-sensitive P2X5 isoforms across diverse species. Through gene profiling and next-generation sequencing (NGS), we found that the zfP2X5TV2 isoform dominates ATP-sensitive forms in zebrafish. In mice, ATP-sensitive mP2X5G317 (mP2X5.1) comprises [~]90% of transcripts, while in rats, exon 3-containing rP2X5F191 accounts for over 70%. In human cell lines, ATP-sensitive isoforms retaining exons 3, 7, and 10 represent [~]15-30% of P2X5 transcripts. RNA-seq from human tissues confirms frequent retention of exons 3 and 7 and polymorphic exon 10 expression. ATP-sensitive P2X5 variants were also identified in chickens, bullfrogs, dogs, cows, and naked mole-rats. These findings challenge the prevailing assumption of ATP-insensitivity, highlighting the need to reassess P2X5s roles in physiological and pathological contexts.