Abstract

Recent studies have suggested that alcohols can affect the function of neurotransmitter-gated ion channels by a direct interaction with the receptor protein. However, the molecular region of the receptor protein that mediates the alcohol action is not known. To address this question, we studied the effect of ethanol on the function of recombinant nicotinic acetylcholine type alpha 7 (nACh alpha 7) receptors, 5-hydroxytryptamine (serotonin) type 3 (5-HT3) receptors, and a chimeric receptor constructed from these two receptors. The receptors were expressed in Xenopus oocytes and their function was studied using the two-electrode voltage-clamp technique. Ethanol inhibited the response of nACh alpha 7 receptors in a concentration-dependent manner over the concentration range of 5-100 mM; the EC50 for this inhibition was 33 mM ethanol. Ethanol decreased the maximal amplitude (Emax) of the nACh alpha 7 receptor agonist concentration-response curve, without significantly affecting the EC50. In contrast, ethanol potentiated 5-HT3 receptor-mediated responses at low agonist concentrations. The potentiation was concentration-dependent over the concentration range of 10-100 mM; the EC50 for this potentiation was 57 mM ethanol. The magnitude of the ethanol potentiation of 5-HT3 receptor-mediated responses decreased with increasing agonist concentration. The chimeric receptor had the amino-terminal domain from the nACh alpha 7 receptor and the transmembrane and carboxyl-terminal domains from the 5-HT3 receptor. Ethanol was found to inhibit the function of this chimeric receptor in a manner similar to that of nACh alpha 7 receptors. Because the inhibition transfers with the amino-terminal domain of the receptor, the observations suggest that the amino-terminal domain of the receptor is involved in the inhibition.