Coexpression of Rat P2X2and P2X6Subunits inXenopusOocytes

Transcripts for P2X2and P2X6subunits are present in rat CNS and frequently colocalize in the same brainstem nuclei. When rat P2X2(rP2X2) and rat P2X6(rP2X6) receptors were expressed individually inXenopusoocytes and studied under voltage-clamp conditions, only homomeric rP2X2receptors were fully functional and gave rise to large inward currents (2–3 μA) to extracellular ATP. Coexpression of rP2X2and rP2X6subunits inXenopusoocytes resulted in a heteromeric rP2X2/6receptor, which showed a significantly different phenotype from the wild-type rP2X2receptor. Differences included reduction in agonist potencies and, in some cases (e.g., Ap4A), significant loss of agonist activity. ATP-evoked inward currents were biphasic at the heteromeric rP2X2/6receptor, particularly when Zn2+ions were present or extracellular pH was lowered. The pH range was narrower for H+enhancement of ATP responses at the heteromeric rP2X2/6receptor. Also, H+ions inhibited ATP responses at low pH levels (2+on ATP responses was unchanged. Thus, the rP2X2/6receptor is a functionally modified P2X2-like receptor with a distinct pattern of pH modulation of ATP activation and suramin blockade. Although homomeric P2X6receptors function poorly, the P2X6subunit can contribute to functional heteromeric P2X channels and may influence the phenotype of native P2X receptors in those cells in which it is expressed.