Abstract
Ethanol can potentiate serotonin type 3 (5-HT(3)) receptor-mediated responses in various neurons and in cells expressing 5-HT(3A) receptors. However, the molecular basis for alcohol modulation of 5-HT(3) receptor function has not been determined. Here we report that point mutations of the arginine at amino acid 222 in the N-terminal domain of the 5-HT(3A) receptor can alter the EC(50) value of the 5-HT concentration-response curve. Some point mutations at amino acid 222 resulted in spontaneous opening of the 5-HT(3A) receptor channel and an inward current activated by ethanol in the absence of agonist. Among these mutant receptors, the amplitude of the current activated by ethanol in the absence of agonist was correlated with the amplitude of the current resulting from spontaneous channel openings, suggesting that the sensitivity of the receptor to ethanol in the absence of agonist is, at least in part, dependent on the preexisting conformational equilibrium of the receptor protein. On the other hand, point mutations that conferred greater sensitivity to ethanol potentiation of agonist-activated responses were less sensitive or insensitive to ethanol in the absence of agonist. For these receptors, the magnitude of the potentiation of agonist-activated responses by ethanol was inversely correlated with the EC(50) values of the 5-HT concentration-response curves, suggesting that these mutations may modulate ethanol sensitivity of the receptor by altering the EC(50) value of the receptor. Thus, distinct molecular processes may determine the sensitivity of 5-HT(3A) receptors to ethanol in the absence and presence of agonist.
Highlights
5-HT3A receptor consists of a large N-terminal domain, four transmembrane domains (TM), and a large intracellular domain [1]
Point mutations of several specific amino acids located in the second and third TMs of glycine and GABAA receptors have been shown to alter the sensitivity of the receptor to ethanol, suggesting that these residues may be crucial for the allosteric modulation of receptor function by ethanol
Functional Characterization of Point Mutations at Residue 222 of 5-HT3A Receptors— molecular cloning has identified two subtypes of 5-HT3 receptors, 5-HT3A and 5-HT3B [1, 30], the 5-HT3A receptor is thought to be an essential component of all serotonin-gated ion channels
Summary
Vol 277, No 48, Issue of November 29, pp. 46256 –46264, 2002 Printed in U.S.A. Distinct Molecular Basis for Differential Sensitivity of the Serotonin Type 3A Receptor to Ethanol in the Absence and Presence of Agonist*. We report that point mutations of the arginine at amino acid 222 in the Nterminal domain of the 5-HT3A receptor can alter the EC50 value of the 5-HT concentration-response curve. Some point mutations at amino acid 222 resulted in spontaneous opening of the 5-HT3A receptor channel and an inward current activated by ethanol in the absence of agonist. Distinct molecular processes may determine the sensitivity of 5-HT3A receptors to ethanol in the absence and presence of agonist. We report that substitutions of an arginine (Arg) with a series of amino acid residues at 222 in the N-terminal domain, immediately preceding TM1 of the 5-HT3A receptor, can alter receptor sensitivity to ethanol and the EC50 value of the 5-HT concentration-response curve. Detailed analyses suggest that the sensitivity of the receptor to ethanol in the absence and presence of agonist may be mediated through different molecular processes. Some of this work has been presented previously in preliminary forms [26, 27]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
