Characteristics of Alpha4/Delta-containing concatemeric GABA(A) receptors expressed in Xenopus oocytes

Shu HJ, Bracamontes J, Taylor A, Wu K, McCollum M, Akk G, Manion B, Evers AS, Krishnan K, Covey DF, Zorumski CF, Steinbach JH, Mennerick S (2011). Br J Pharmacol, doi:10.1111/j. 1476-5381
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Background and purpose.  GABA(A) receptors mediate both synaptic and extrasynaptic actions of GABA. In several neuronal populations, α4 and δ subunits are key components of extrasynaptic GABA(A) receptors that strongly influence neuronal excitability and could mediate the effects of neuroactive agents including neurosteroids and ethanol. However, these receptors can be difficult to study in native cells, and recombinant δ subunits can be difficult to express in heterologous systems. Experimental approach.  We took the approach of engineering concatemeric (fused) subunits to help ensure δ and α4 subunit expression. We tested the pharmacology of the concatemeric receptors, compared with a common synaptic-like receptor subunit combination (α1 +β2 +γ2L), and with free-subunit α4/δ receptors. Key results.  δ-β2-α4 +β2-α4 cRNA co-injected into Xenopus oocytes resulted in GABA-gated currents with the expected major pharmacological properties of α4/δ-containing receptors. Criteria included sensitivity to agonists of different efficacy, sensitivity to the allosteric activator pentobarbital, and modulation of agonist responses by DS2 (4-chloro-N-[2-(2-thienyl)imidazo[1,2-a]pyridine-3-yl benzamide; a δ-selective positive modulator), furosemide, and Zn(2+) . We used the concatemers to examine neurosteroid sensitivity of extrasynaptic-like, δ-containing receptors. We found no qualitative differences between extrasynaptic-like receptors and synaptic-like receptors in the actions of either negative or positive neurosteroid modulators of receptor function. Quantitative differences were explained by the partial agonist effects of the natural agonist GABA and by a mildly increased sensitivity to low steroid concentrations. Conclusions and Implications.  We conclude that neurosteroid structure-activity profile for α4/δ-containing extrasynaptic receptors is unlikely to differ from that of synaptic-like receptors such as α1/β2/γ2-containing receptors.

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Posted on October 17, 2011
Posted in: HPAN, Neurodegeneration, Publications Authors: , ,