RT Journal Article SR Electronic T1 Ethanol Stabilizes the Open State of Single 5-Hydroxytryptamine3A(QDA) Receptors JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 896 OP 902 DO 10.1124/jpet.109.164863 VO 333 IS 3 A1 Paula L. Feinberg-Zadek A1 Paul A. Davies YR 2010 UL http://jpet.aspetjournals.org/content/333/3/896.abstract AB Ethanol enhancement of 5-hydroxytryptamine (5-HT)3A receptor-mediated responses may have important consequences in the intoxicating and addictive properties of ethanol. Although the exact mechanism is unknown, ethanol-mediated enhancement of 5-HT3 receptor current has been proposed to occur due to stabilization of the open-channel state. It has not been possible to directly measure the open state of the channel due to the extremely low single-channel conductance of 5-HT3A channels. Recently, three arginine residues within the large intracellular loop of the 5-HT3A subunit were substituted by their equivalent residues (glutamine, aspartate, and alanine) of the 5-HT3B subunit to produce a 5-HT3A(QDA) subunit that forms functional homomeric channels exhibiting a measurable single-channel conductance. Using whole-cell rapid-agonist application techniques and the cell-attached single-channel recording configuration, we examined human 5-HT3A(QDA) receptors expressed in human embryonic kidney 293 cells. The agonist sensitivity, macroscopic kinetics, and modulation by ethanol were similar between mutant and wild-type channels, suggesting the substitutions had not altered these channel structure-function properties. The open time histogram for single-channel events mediated by 5-HT3A(QDA) receptors in the presence of maximal 5-HT was best fit by three exponentials, but in the presence of ethanol a fourth open state was evident. In summary, the QDA substitution greatly enhanced single-channel conductance with little effect on 5-HT3A channel's kinetic properties and ethanol enhances agonist action on 5-HT3A receptors by inducing a new, long-lived open-channel state. Furthermore, the 5-HT3A(QDA) receptor appears to be suitable for pharmacological studies of 5-HT3A receptor modulation at a single-channel level. Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics