title: Dihydropyridine inhibition of the glycine receptor: subunit selectivity and a molecular determinant of inhibition.
abstract: The dihydropyridines (DHPs), nifedipine and nicardipine, modulate native glycine receptors (GlyRs) at micromolar concentrations. Nicardipine has a biphasic potentiating and inhibitory effect, whereas nifedipine causes inhibition only. The present study sought to investigate (1) the molecular mechanism by which these compounds inhibit recombinant GlyRs, and (2) their potential utility as subunit-selective inhibitors of alpha1, alpha1beta, alpha3 and alpha3beta GlyRs. The rate of onset of inhibition in the open state was accelerated by pre-application of DHP in the closed state, with the degree of acceleration proportional to the concentration of pre-applied DHP. This implies a non-inhibitory binding site close to the DHP inhibitory site. DHP inhibition was use-dependent and independent of glycine concentration, consistent with a pore-blocking mode of action. DHP sensitivity was abolished by the G2'A mutation, providing a strong case for a DHP binding site in the pore. Nifedipine exhibited an approximately 10-fold higher inhibitory potency at alpha1-containing relative to alpha3-containing receptors, whereas nicardipine was only weakly selective for alpha1-containing GlyRs. The differential sensitivities of nifedipine and nicardipine for different GlyR isoforms suggest that DHPs may be a useful resource to screen as pharmacological tools for selectively inhibiting different synaptic GlyR isoforms.
authors.affiliation: School of Biomedical Sciences and Queensland Brain Institute, University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Xuebin
authors.initials: X
authors.lastname: Chen
authors.forename: Brett
authors.initials: B
authors.lastname: Cromer
authors.forename: Timothy I
authors.initials: TI
authors.lastname: Webb
authors.forename: Zhe
authors.initials: Z
authors.lastname: Yang
authors.forename: Janina
authors.initials: J
authors.lastname: Hantke
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Harvey
authors.forename: Michael W
authors.initials: MW
authors.lastname: Parker
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Lynch
mesh_terms: D000595:Amino Acid Sequence; D000704:Analysis of Variance; D001665:Binding Sites / Q000187:drug effects / Q000235:genetics; D055592:Biophysical Phenomena; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002461:Cell Line, Transformed; D004095:Dihydropyridines / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D018756:GABA Antagonists / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed / Q000379:methods; D018408:Patch-Clamp Techniques; D010852:Picrotoxin / Q000031:analogs & derivatives / Q000494:pharmacology; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D018009:Receptors, Glycine / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D054830:Sesterterpenes; D013329:Structure-Activity Relationship
chemical_list: D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D018756:GABA Antagonists; D010852:Picrotoxin; D021122:Protein Subunits; D018009:Receptors, Glycine; D054830:Sesterterpenes; C038806:1,4-dihydropyridine; C022961:picrotoxinin