title: Pharmacological characterisation of murine α4β1δ GABAA receptors expressed in Xenopus oocytes.
abstract: BACKGROUND
  GABAA receptor subunit composition has a profound effect on the receptor's physiological and pharmacological properties. The receptor β subunit is widely recognised for its importance in receptor assembly, trafficking and post-translational modifications, but its influence on extrasynaptic GABAA receptor function is less well understood. Here, we examine the pharmacological properties of a potentially native extrasynaptic GABAA receptor that incorporates the β1 subunit, specifically composed of α4β1δ and α4β1 subunits.
  
  
  RESULTS
  GABA activated concentration-dependent responses at α4β1δ and α4β1 receptors with EC50 values in the nanomolar to micromolar range, respectively. The divalent cations Zn(2+) and Cu(2+), and the β1-selective inhibitor salicylidine salicylhydrazide (SCS), inhibited GABA-activated currents at α4β1δ receptors. Surprisingly the α4β1 receptor demonstrated biphasic sensitivity to Zn(2+) inhibition that may reflect variable subunit stoichiometries with differing sensitivity to Zn(2+). The neurosteroid tetrahydro-deoxycorticosterone (THDOC) significantly increased GABA-initiated responses in concentrations above 30 nM for α4β1δ receptors.
  
  
  CONCLUSIONS
  With this study we report the first pharmacological characterisation of various GABAA receptor ligands acting at murine α4β1δ GABAA receptors, thereby improving our understanding of the molecular pharmacology of this receptor isoform. This study highlights some notable differences in the pharmacology of murine and human α4β1δ receptors. We consider the likelihood that the α4β1δ receptor may play a role as an extrasynaptic GABAA receptor in the nervous system.
authors.affiliation: Department of Neuroscience, Physiology & Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK. inge_villumsen@hotmail.com.|Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Fruebjergvej 3, 2100, Copenhagen, Denmark. inge_villumsen@hotmail.com.
authors.forename: Inge S
authors.initials: IS
authors.lastname: Villumsen
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Fruebjergvej 3, 2100, Copenhagen, Denmark. pw@sund.ku.dk.
authors.forename: Petrine
authors.initials: P
authors.lastname: Wellendorph
authors.affiliation: Department of Neuroscience, Physiology & Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK. t.smart@ucl.ac.uk.
authors.forename: Trevor G
authors.initials: TG
authors.lastname: Smart
mesh_terms: D000818:Animals; D002413:Cations, Divalent / Q000494:pharmacology; D003300:Copper / Q000494:pharmacology; D003900:Desoxycorticosterone / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D051379:Mice; D009865:Oocytes; D018408:Patch-Clamp Techniques; D051381:Rats; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis; D015032:Zinc / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D002413:Cations, Divalent; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; C546261:Gabra4 protein, mouse; C546266:Gabrb1 protein, mouse; C000592156:Gabrd protein, rat; D011963:Receptors, GABA-A; D003900:Desoxycorticosterone; C009413:tetrahydrodeoxycorticosterone; D005680:gamma-Aminobutyric Acid; D003300:Copper; D015032:Zinc