title: Mechanisms for picrotoxinin and picrotin blocks of alpha2 homomeric glycine receptors.
abstract: Contrary to its effect on the gamma-aminobutyric acid type A and C receptors, picrotoxin antagonism of the alpha1 homomeric glycine receptors (GlyRs) has been shown to be non-use-dependent and nonselective between the picrotoxin components picrotoxinin and picrotin. Picrotoxin antagonism of the embryonic alpha2 homomeric GlyR is known to be use-dependent and reflects a channel-blocking mechanism, but the selectivity of picrotoxin antagonism of the embryonic alpha2 homomeric GlyRs between picrotoxinin and picrotin is unknown. Hence, we used the patch clamp recording technique in the outside-out configuration to investigate, at the single channel level, the mechanism of picrotin- and picrotoxinin-induced inhibition of currents, which were evoked by the activation of alpha2 homomeric GlyRs stably transfected into Chinese hamster ovary cells. Although both picrotoxinin and picrotin inhibited glycine-evoked outside-out currents, picrotin had a 30 times higher IC50 than picrotoxinin. Picrotin-evoked inhibition displayed voltage dependence, whereas picrotoxinin did not. Picrotoxinin and picrotin decreased the mean open time of the channel in a concentration-dependent manner, indicating that these picrotoxin components can bind to the receptor in its open state. When picrotin and glycine were co-applied, a large rebound current was observed at the end of the application. This rebound current was considerably smaller when picrotoxinin and glycine were co-applied. Both picrotin and picrotoxinin were unable to bind to the unbound conformation of the receptor, but both could be trapped at their binding site when the channel closed during glycine dissociation. Our data indicate that picrotoxinin and picrotin are not equivalent in blocking alpha2 homomeric GlyR.
authors.affiliation: UMR CNRS 7102 Neurobiologie des Processus Adaptatifs, Université Pierre et Marie Curie, 9 Quai St. Bernard, 75252, Paris Cedex 05, France, and Center for Neuroscience Research, Children's National Medical Center, Washington DC 20010, USA.
authors.forename: Dian-Shi
authors.initials: DS
authors.lastname: Wang
authors.forename: Roeland
authors.initials: R
authors.lastname: Buckinx
authors.forename: Hervé
authors.initials: H
authors.lastname: Lecorronc
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Mangin
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Rigo
authors.forename: Pascal
authors.initials: P
authors.lastname: Legendre
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D005071:Evoked Potentials / Q000187:drug effects*; D018756:GABA Antagonists / Q000494:pharmacology*; D005998:Glycine / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010852:Picrotoxin / Q000031:analogs & derivatives* / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011487:Protein Conformation / Q000187:drug effects; D018009:Receptors, Glycine / Q000037:antagonists & inhibitors* / Q000235:genetics; D054830:Sesterterpenes; D014162:Transfection
chemical_list: D018756:GABA Antagonists; D005998:Glycine; D010852:Picrotoxin; D018009:Receptors, Glycine; D054830:Sesterterpenes; C439504:GLRA2 protein, human; C022961:picrotoxinin; C411705:picrotin