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A study of subunit selectivity, mechanism and site of action of the delta selective compound 2 ( DS2 ) at human recombinant and rodent native GABA A receptors
Author(s) -
Jensen ML,
Wafford KA,
Brown AR,
Belelli D,
Lambert JJ,
Mirza NR
Publication year - 2013
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/bph.12001
Subject(s) - receptor , gabaa receptor , allosteric regulation , allosteric modulator , pharmacology , ionotropic effect , mechanism of action , chemistry , protein subunit , gabaa rho receptor , neuroscience , biology , biochemistry , glutamate receptor , in vitro , gene
Background and Purpose Most GABA A receptor subtypes comprise 2α, 2β and 1γ subunit, although for some isoforms, a δ replaces a γ‐subunit. Extrasynaptic δ‐ GABA A receptors are important therapeutic targets, but there are few suitable pharmacological tools. We profiled DS2 , the purported positive allosteric modulator ( PAM ) of δ‐ GABA A receptors to better understand subtype selectivity, mechanism/site of action and activity at native δ‐ GABA A receptors. Experimental Approach Subunit specificity of DS2 was determined using electrophysiological recordings of X enopus laevis oocytes expressing human recombinant GABA A receptor isoforms. Effects of DS2 on GABA concentration–response curves were assessed to define mechanisms of action. Radioligand binding and electrophysiology utilising mutant receptors and pharmacology were used to define site of action. Using brain‐slice electrophysiology, we assessed the influence of DS2 on thalamic inhibition in wild‐type and δ 0/0 mice. Key Results Actions of DS2 were primarily determined by the δ‐subunit but were additionally influenced by the α, but not the β, subunit (α4/6βxδ > α1βxδ >> γ2‐GABA A receptors > α4β3). For δ‐GABA A receptors, DS2 enhanced maximum responses to GABA , with minimal influence on GABA potency. (iii) DS2 did not act via the orthosteric, or known modulatory sites on GABA A receptors. (iv) DS2 enhanced tonic currents of thalamocortical neurones from wild‐type but not δ 0/0 mice. Conclusions and Implications DS2 is the first PAM selective for α4/6βxδ receptors, providing a novel tool to investigate extrasynaptic δ‐GABA A receptors. The effects of DS2 are mediated by an unknown site leading to GABA A receptor isoform selectivity.