We have used patch-clamp recording from cultured neurones, immunohistochemistry and gene deletion techniques to characterize the P2X receptors present in mouse otic
ganglion neurones, and demonstrated the presence of similar receptors in rat neurones. All neurones from wild-type (WT) mice responded to
ATP (EC(50) 109 microM), but only 38% also responded to
alpha beta-meATP (EC(50) 39 microM). The response to
alpha beta-meATP was blocked by
TNP-ATP with an IC(50) of 38.6 nM. Lowering extracellular pH and co-application of Zn(2+) potentiated responses to
ATP and
alpha beta-meATP. In P2X(3)(-/-) mouse otic
ganglion, all neurones tested responded to 100 microM
ATP with a sustained current, but none responded to
alpha beta-meATP. In P2X(2)(-/-) mice, no sustained currents were observed, but 36% of neurones responded to both
ATP and
alpha beta-meATP with transient currents. In P2X(2)/P2X(3)(Dbl-/-) mice, no responses to
ATP or
alpha beta-meATP were detected, suggesting that other P2X subunits were not involved. In rat otic ganglia, 96% of neurones responded to both
ATP and
alpha beta-meATP with sustained currents, suggesting a greater proportion of neurones expressing P2X(2/3) receptors. The maximum response to
alpha beta-meATP was 40-60% of that evoked by
ATP in the same cell. Immunohistochemistry revealed staining for P2X(2) and P2X(3) subunits in WT mouse otic
ganglion neurones, which was absent in knockout animals. In conclusion, we have shown for the first time that at least two distinct P2X receptors are present in mouse and rat otic neurones, probably homomeric P2X(2) and heteromeric P2X(2/3) receptors.