title: Identification of a domain which affects kinetics and antagonistic potency of clozapine at 5-HT3 receptors.
abstract: The widely used atypical antipsychotic clozapine is a potent competitive antagonist at 5-HT(3) receptors which may contribute to its unique psychopharmacological profile. Clozapine binds to 5-HT(3) receptors of various species. However, the structural requirements of the respective binding site for clozapine remain to be determined. Differences in the primary sequences within the 5-HT(3A) receptor gene in schizophrenic patients may result in an alteration of the antipsychotic potency and/or the side effect profile of clozapine. To determine these structural requirements we constructed chimeras with different 5-HT(3A) receptor sequences of murine and human origin and expressed these mutants in human embryonic kidney (HEK) 293 cells. Clozapine antagonises recombinant mouse 5-HT(3A) receptors with higher potency compared to recombinant human 5-HT(3A) receptors. 5-HT activation curves and clozapine inhibition curves yielded the parameters EC(50) and IC(50) for all receptors tested in the range of 0.6 - 2.7 microM and 1.5 - 83.3 nM, respectively. The use of the Cheng-Prusoff equation to calculate the dissociation constant K(b) values for clozapine revealed that an extracellular sequence (length 86 aa) close to the transmembrane domain M1 strongly determines the binding affinity of clozapine. K(b) values of clozapine were significantly lower (0.3-1.1 nM) for receptors containing the murine sequence and higher when compared with receptors containing the respective human sequence (5.8-13.4 nM). Thus, individual differences in the primary sequence of 5-HT(3) receptors may be crucial for the antipsychotic potency and/or the side effect profile of clozapine.
authors.affiliation: Max Planck Institute of Psychiatry, Munich, Germany. rammes@mpipsykl.mpg.de
authors.forename: Gerhard
authors.initials: G
authors.lastname: Rammes
authors.forename: Christine
authors.initials: C
authors.lastname: Hosp
authors.forename: Brigitte
authors.initials: B
authors.lastname: Eisensamer
authors.forename: Sascha
authors.initials: S
authors.lastname: Tanasic
authors.forename: Caroline
authors.initials: C
authors.lastname: Nothdurfter
authors.forename: Walter
authors.initials: W
authors.lastname: Zieglgänsberger
authors.forename: Rainer
authors.initials: R
authors.lastname: Rupprecht
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D014150:Antipsychotic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D002460:Cell Line; D003024:Clozapine / Q000493:pharmacokinetics / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D044406:Receptors, Serotonin, 5-HT3 / Q000737:chemistry; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors; D017386:Sequence Homology, Amino Acid; D058831:Serotonin 5-HT3 Receptor Antagonists
chemical_list: D014150:Antipsychotic Agents; D044406:Receptors, Serotonin, 5-HT3; D011994:Recombinant Proteins; D058831:Serotonin 5-HT3 Receptor Antagonists; D003024:Clozapine
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