Co-expression of P2X1 and P2X5 receptor subunits reveals a novel ATP-gated ion channel

P2X receptors are a family of ion channels gated by extracellular ATP. Each member of the family can form functional homomeric channels, but only P2X(2) and P2X(3) have been shown to combine to form a unique heteromeric channel. Data from in situ hybridization studies suggest that P2X(1) and P2X(5) may also co-assemble. In this study, we tested this hypothesis by expressing recombinant P2X(1) and P2X(5) receptor subunits either individually or together in human embryonic kidney 293 cells. In cells expressing the homomeric P2X(1) receptor, 30 mu M alpha,beta-methylene ATP (alpha,beta-me-ATP) evoked robust currents that completely desensitized in less than 1 sec, whereas alpha,beta-me-ATP failed to evoke current in cells expressing the homomeric P2X(5) receptor. By contrast, alpha,beta-me-ATP evoked biphasic currents with a pronounced nondesensitizing plateau phase in cells that co-expressed both subunits. Further, the EC50 for alpha,beta-me-ATP was greater in cells expressing both P2X(1) and P2X(5) than in cells expressing P2X(1) alone (5 and 1.6 mu M, respectively). Heteromeric assembly was confirmed using a coimmunoprecipitation assay of epitope-tagged P2X(1) and P2X(5) subunits. In summary, this study provides biochemical and functional evidence of a novel channel formed by P2X subunit heteropolymerization. This finding suggests that heteromeric subunit assembly constitutes an important mechanism for generating functional diversity of ATP-mediated responses.