Hydrophobic anions potently and uncompetitively antagonize GABA A receptor function in the absence of a conventional binding site

M. Chisari, K. Wu, C. F. Zorumski, S. Mennerick

Research output: Contribution to journalArticle

13 Scopus citations

Abstract

BACKGROUND AND PURPOSE A 'lock-and-key' binding site typically accounts for the effect of receptor antagonists. However, sulphated neurosteroids are potent non-competitive antagonists of GABA A receptors without a clear structure-activity relationship. To gain new insights, we tested two structurally unrelated hydrophobic anions with superficially similar properties to sulphated neurosteroids. EXPERIMENTAL APPROACH We used voltage-clamp techniques in Xenopus oocytes and hippocampal neurons to characterize dipicrylamine (DPA) and tetraphenylborate (TPB), compounds previously used to probe membrane structure and voltage-gated ion channel function. KEY RESULTS Both DPA and TPB potently antagonized GABA A receptors. DPA exhibited an IC 50 near 60 nM at half-maximal GABA concentration and antagonism with features indistinguishable from pregnenolone sulphate antagonism, including sensitivity to a point mutation in transmembrane domain 2 of the α1 subunit. Bovine serum albumin, which scavenges free membrane-associated DPA, accelerated both capacitance offset and antagonism washout. Membrane interactions and antagonism were explored using the voltage-dependent movement of DPA between membrane leaflets. Washout of DPA antagonism was strongly voltage-dependent, paralleling DPA membrane loss, although steady-state antagonism lacked voltage dependence. At antagonist concentrations, DPA failed to affect inhibitory post-synaptic current (IPSC) amplitude or decay, but DPA accelerated pharmacologically prolonged IPSCs. CONCLUSIONS AND IMPLICATIONS Neurosteroid-like GABA A receptor antagonism appears to lacks a conventional binding site. These features highlight key roles of membrane interactions in antagonism. Because its membrane mobility can be controlled, DPA may be a useful probe of GABA A receptors, but its effects on excitability via GABA A receptors raise caveats for its use in monitoring neuronal activity.

Original languageEnglish
Pages (from-to)667-680
Number of pages14
JournalBritish Journal of Pharmacology
Volume164
Issue number2 B
DOIs
StatePublished - Sep 1 2011

Keywords

  • GABA receptors
  • antagonist
  • hippocampal
  • membrane capacitance
  • voltage sensor

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