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Br J Pharmacol. 2011 Sep;164(2b):667-80. doi: 10.1111/j.1476-5381.2011.01396.x.

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

Author information

1
Departments of Psychiatry Anatomy & Neurobiology, Washington University School of Medicine, St. Louis, MO, USA.

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 IC₅₀ 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.

PMID:
21457224
PMCID:
PMC3188920
DOI:
10.1111/j.1476-5381.2011.01396.x
[Indexed for MEDLINE]
Free PMC Article

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