Ethanol sensitivity in ATP-Gated P2X receptors is subunit dependent

Background: P2X receptors are ligand-gated cation channels that are gated by synaptically released extracellular adenosine 5'-triphosphate (ATP). P2X receptors are inhibited by ethanol; however, few investigations have focused on ethanol's effects in P2X receptors. Recently, recombinant homomeric P2X(4) receptors were reported to be sensitive to ethanol's inhibitory action, whereas recombinant P2X(3) receptors were insensitive to ethanol. The two recombinant studies were conducted in different expression systems by using different techniques; therefore, questions remain. The present study tests the hypothesis that ethanol sensitivity in P2X receptors is subunit dependent. Methods: The effects of ethanol (25-200 mM+/-ATP) on rat recombinant homomeric P2X(2) and P2X(4) receptors expressed in Xenopus oocytes were tested by using two-electrode voltage clamp techniques. Results: Ethanol inhibited EC10 ATP-gated currents significantly-less in P2X(2) versus P2X(4) receptors. A second study found that ethanol right-shifted the ATP concentration-response curve in P2X(2) receptors, which significantly increased the EC50 for ATP without altering the Hill slope or maximal current response to ATP. These latter characteristics of ethanol action in P2X(2) receptors agree with previous work in P2X(4) receptors. There was no effect of ethanol when tested in the absence of ATP. Conclusion: The findings are the first to show (1) ethanol inhibition of ATP-activated currents on P2X(2) receptors, (2) differences in ethanol sensitivity between homomeric P2X receptors when tested under matched conditions, and (3) evidence that suggests similar mechanisms of ethanol action for P2X(2) and P2X(4) receptors. These findings provide the first direct support for the hypothesis that ethanol sensitivity in P2X receptors is subunit dependent.