title: Inhibitory effects of dextrorotatory morphinans on the human 5-HT(3A) receptor expressed in Xenopus oocytes: Involvement of the N-terminal domain of the 5-HT(3A) receptor.
abstract: We previously developed a series of dextromethorphan (DM, 3-methoxy-17-methylmorphinan) analogs modified at positions 3 and 17 of the morphinan ring system. Recent reports have shown that DM attenuates abdominal pain caused by irritable bowel syndrome, and multidrug regimens that include DM prevent nausea/vomiting following cancer surgery. However, little is known regarding the molecular mechanisms underlying the beneficial effects of DM. Here, we investigated the effects of DM, 3 of its analogs (AM, 3-allyloxy-17-methoxymorphian; CM, 3-cyclopropyl-17-methoxymorphinan; and DF, 3-methyl-17-methylmorphinan), and 1 of its metabolites (HM, 3-methoxymorphinan) on the activity of the human 5-HT(3A) receptor channel expressed in Xenopus laevis oocytes, using the 2-microelectrode voltage clamp technique. We found that intra-oocyte injection of human 5-HT(3A) receptor cRNAs elicited an inward current (I(5-HT)) in the presence of 5-HT. Cotreatment with AM, CM, DF, DM, or HM inhibited I(5-HT) in a dose-dependent, voltage-independent, and reversible manner. The IC(50) values for AM, CM, DF, DM, and HM were 24.5±1.4, 21.5±4.2, 132.6±35.8, 181.3±23.5, and 191.3±31.5μM, respectively. The IC(50) values of AM and CM were 7-fold lower than that of DM, and mechanistic analysis revealed that DM, DF, HM, AM, and CM were competitive inhibitors of I(5-HT). Point mutations of Arg241 in the N-terminal, but not amino acids in the pore region, to other amino acid residues attenuated or abolished DM- and DM-analog-induced inhibition of I(5-HT). Together, these results demonstrated that dextrorotatory morphinans might regulate 5-HT(3A) receptor channel activity via interaction with its N-terminal domain.
authors.affiliation: Department of Physiology, College of Veterinary Medicine, Bio/Molecular Informatics Center, Konkuk University, Seoul, Republic of Korea.
authors.forename: Byung-Hwan
authors.initials: BH
authors.lastname: Lee
authors.forename: Sung-Hee
authors.initials: SH
authors.lastname: Hwang
authors.forename: Sun-Hye
authors.initials: SH
authors.lastname: Choi
authors.forename: Tae-Joon
authors.initials: TJ
authors.lastname: Shin
authors.forename: Jiyeon
authors.initials: J
authors.lastname: Kang
authors.forename: Hyun-Joong
authors.initials: HJ
authors.lastname: Kim
authors.forename: Hyoung-Chun
authors.initials: HC
authors.lastname: Kim
authors.forename: Joon-Hee
authors.initials: JH
authors.lastname: Lee
authors.forename: Seung-Yeol
authors.initials: SY
authors.lastname: Nah
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D006801:Humans; D009019:Morphinans / Q000494:pharmacology*; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D044406:Receptors, Serotonin, 5-HT3 / Q000737:chemistry / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: C509409:HTR3A protein, human; D009019:Morphinans; D044406:Receptors, Serotonin, 5-HT3