title: Zolpidem and eszopiclone prime α1β2γ2 GABAA receptors for longer duration of activity.
abstract: OBJECTIVE
  GABAA receptors mediate neuronal inhibition in the brain. They are the primary targets for benzodiazepines, which are widely used to treat neurological disorders including anxiety, epilepsy and insomnia. The mechanism by which benzodiazepines enhance GABAA receptor activity has been extensively studied, but there is little mechanistic information on how non-benzodiazepine drugs that bind to the same site exert their effects. Eszopiclone and zolpidem are two non-benzodiazepine drugs for which no mechanism of action has yet been proposed, despite their clinical importance as sleeping aids. Here we investigate how both drugs enhance the activity of α1β2γ2 GABAA receptors.
  
  
  METHODS
  We used rapid ligand application onto macropatches and single-channel kinetic analysis to assess rates of current deactivation. We also studied synaptic currents in primary neuronal cultures and in heterosynapses, whereby native GABAergic nerve terminals form synapses with HEK293 cells expressing α1β2γ2 GABAA receptors. Drug binding and modulation was quantified with the aid of an activation mechanism.
  
  
  RESULTS
  At the single-channel level, the drugs prolonged the duration of receptor activation, with similar KD values of ∼80 nM. Channel activation was prolonged primarily by increasing the equilibrium constant between two connected shut states that precede channel opening.
  
  
  CONCLUSIONS
  As the derived mechanism successfully simulated the effects of eszopiclone and zolpidem on ensemble currents, we propose it as the definitive mechanism accounting for the effects of both drugs. Importantly, eszopiclone and zolpidem enhanced GABAA receptor currents via a mechanism that differs from that proposed for benzodiazepines.
authors: Queensland Brain Institute, University of Queensland, Brisbane, Qld, Australia.
authors: Christine L
authors: CL
authors: Dixon
authors: Department of Anesthesiology and Department of Pharmacology, Columbia University, New York, NY, USA.
authors: Neil L
authors: NL
authors: Harrison
authors: Queensland Brain Institute, University of Queensland, Brisbane, Qld, Australia.|School of Biomedical Sciences, University of Queensland, Brisbane, Qld, Australia.
authors: Joseph W
authors: JW
authors: Lynch
authors: Queensland Brain Institute, University of Queensland, Brisbane, Qld, Australia.|Department of Anesthesiology and Department of Pharmacology, Columbia University, New York, NY, USA.
authors: Angelo
authors: A
authors: Keramidas
mesh_terms: D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D000069582:Eszopiclone / Q000494:pharmacology*; D057809:HEK293 Cells; D006801:Humans; D011725:Pyridines / Q000494:pharmacology*; D011963:Receptors, GABA-A / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013997:Time Factors; D000077334:Zolpidem
chemical_list: C546240:GABRA1 protein, human; C495710:GABRB2 protein, human; C546279:GABRG2 protein, human; D011725:Pyridines; D011963:Receptors, GABA-A; D000077334:Zolpidem; D000069582:Eszopiclone