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 P2X⁴ receptors were reported to be sensitive to ethanol's inhibitory action, whereas recombinant P2X₃ 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 P2X₂ and P2X₄ receptors expressed in Xenopus oocytes were tested by using two-electrode voltage clamp techniques. Results: Ethanol inhibited EC₁₀ ATP-gated currents significantly less in P2X₂ versus P2X₄ receptors. A second study found that ethanol right-shifted the ATP concentration-response curve in P2X₂ 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 P2X₂ receptors agree with previous work in P2X₄ 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 P2X₂ 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 P2X₂ and P2X₄ receptors. These findings provide the first direct support for the hypothesis that ethanol sensitivity in P2X receptors is subunit dependent.