Dataset Information

Orthosteric- versus allosteric-dependent activation of the GABAA receptor requires numerically distinct subunit level rearrangements.

ABSTRACT: Anaesthetic molecules act on synaptic transmission via the allosteric modulation of ligand-gated chloride channels, such as hetero-oligomeric ?1?2?2 GABAA receptors. To elucidate the overall activation paradigm via allosteric versus orthosteric sites, we used highly homologous, but homo-oligomeric, ?1 receptors that are contrastingly insensitive to anaesthetics and respond partially to several full GABA ?1?2?2 receptor agonists. Here, we coexpressed varying ratios of RNAs encoding the wild-type and the mutated ?1 subunits, which are anaesthetic-sensitive and respond with full efficacy to partial GABA agonists, to generate distinct ensembles of receptors containing five, four, three, two, one, or zero mutated subunits. Using these experiments, we then demonstrate that, in the pentamer, three anaesthetic-sensitive ?1 subunits are needed to impart full efficacy to the partial GABA agonists. By contrast, five anaesthetic-sensitive subunits are required for direct activation by anaesthetics alone, and only one anaesthetic-sensitive subunit is sufficient to confer the anaesthetic-dependent potentiation to the GABA current. In conclusion, our data indicate that GABA and anaesthetics holistically activate the GABAA ?1 receptor through distinct subunit level rearrangements and suggest that in contrast to the global impact of GABA via orthosteric sites, the force of anaesthetics through allosteric sites may not propagate to the neighbouring subunits and, thus, may have only a local and limited effect on the ?1 GABAA receptor model system.

SUBMITTER: Amin J

PROVIDER: S-EPMC5552871 | biostudies-other | 2017 Aug

REPOSITORIES: biostudies-other

ACCESS DATA

Publications

Orthosteric- versus allosteric-dependent activation of the GABAA receptor requires numerically distinct subunit level rearrangements.

Amin Jahanshah J Subbarayan Meena S MS

Scientific reports 20170810 1

Anaesthetic molecules act on synaptic transmission via the allosteric modulation of ligand-gated chloride channels, such as hetero-oligomeric α1β2γ2 GABAA receptors. To elucidate the overall activation paradigm via allosteric versus orthosteric sites, we used highly homologous, but homo-oligomeric, ρ1 receptors that are contrastingly insensitive to anaesthetics and respond partially to several full GABA α1β2γ2</sub ...[more]

PMID: 28798394

Similar Datasets

Project description:Valerenic acid (VA)-a ?2/3-selective GABA type A (GABAA) receptor modulator-displays anxiolytic and anticonvulsive effects in mice devoid of sedation, making VA an interesting drug candidate. Here we analyzed ?-subunit-dependent enhancement of GABA-induced chloride currents (IGABA) by a library of VA derivatives and studied their effects on pentylenetetrazole (PTZ)-induced seizure threshold and locomotion. Compound-induced IGABA enhancement was determined in oocytes expressing ?1?1?2S, ?1?2?2S, or ?1?3?2S receptors. Effects on seizure threshold and locomotion were studied using C57BL/6N mice and compared with saline-treated controls. ?2/3-selective VA derivatives such as VA-amide (VA-A) modulating ?1?3?2S (VA-A: Emax = 972 ± 69%, n = 6, P < 0.05) and ?1?2?2S receptors (Emax = 1119 ± 72%, n = 6, P < 0.05) more efficaciously than VA (?1?3?2S: VA: Emax = 632 ± 88%, n = 9 versus ?1?2?2S: VA: Emax = 721 ± 68%, n = 6) displayed significantly more pronounced seizure threshold elevation than VA (saline control: 40.4 ± 1.4 mg/kg PTZ versus VA 10 mg/kg: 49.0 ± 1.8 mg/kg PTZ versus VA-A 3 mg/kg: 57.9 ± 1.9 mg/kg PTZ, P < 0.05). Similarly, VA's methylamide (VA-MA) enhancing IGABA through ?3-containing receptors more efficaciously than VA (Emax = 1043 ± 57%, P < 0.01, n = 6) displayed stronger anticonvulsive effects. Increased potency of IGABA enhancement and anticonvulsive effects at lower doses compared with VA were observed for VA-tetrazole (?1?3?2S: VA-TET: EC50 = 6.0 ± 1.0 ?M, P < 0.05; VA-TET: 0.3 mg/kg: 47.3 ± 0.5 mg/kg PTZ versus VA: 10 mg/kg: 49.0 ± 1.8 mg/kg PTZ, P < 0.05). At higher doses (?10 mg/kg), VA-A, VA-MA, and VA-TET reduced locomotion. In contrast, unselective VA derivatives induced anticonvulsive effects only at high doses (30 mg/kg) or did not display any behavioral effects. Our data indicate that the ?2/3-selective compounds VA-A, VA-MA, and VA-TET induce anticonvulsive effects at low doses (?10 mg/kg), whereas impairment of locomotion was observed at doses ?10 mg/kg.

Project description:Phasic GABAergic inhibition in hippocampus and neocortex falls into two kinetically distinct categories, GABA(A,fast) and GABA(A,slow). In hippocampal area CA1, GABA(A,fast) is generally believed to underlie gamma oscillations, whereas the contribution of GABA(A,slow) to hippocampal rhythms has been speculative. Hypothesizing that GABA(A) receptors containing the beta(3) subunit contribute to GABA(A,slow) inhibition and that slow inhibitory synapses control excitability as well as contribute to network rhythms, we investigated the consequences of this subunit's absence on synaptic inhibition and network function. In pyramidal neurons of GABA(A) receptor beta(3) subunit-deficient (beta(3)(-/-)) mice, spontaneous GABA(A,slow) inhibitory postsynaptic currents (IPSCs) were much less frequent, and evoked GABA(A,slow) currents were much smaller than in wild-type mice. Fittingly, long-lasting recurrent inhibition of population spikes was less powerful in the mutant, indicating that receptors containing beta(3) subunits contribute substantially to GABA(A,slow) currents in pyramidal neurons. By contrast, slow inhibitory control of GABA(A,fast)-producing interneurons was unaffected in beta(3)(-/-) mice. In vivo hippocampal network activity was markedly different in the two genotypes. In beta(3)(-/-) mice, epileptiform activity was observed, and theta oscillations were weaker, slower, less regular and less well coordinated across laminae compared with wild-type mice, whereas gamma oscillations were weaker and faster. The amplitude modulation of gamma oscillations at theta frequency ("nesting") was preserved but was less well coordinated with theta oscillations. With the caveat that seizure-induced changes in inhibitory circuits might have contributed to the changes observed in the mutant animals, our results point to a strong contribution of beta(3) subunits to slow GABAergic inhibition onto pyramidal neurons but not onto GABA(A,fast) -producing interneurons and support different roles for these slow inhibitory synapses in the generation and coordination of hippocampal network rhythms.

Dataset Information

Orthosteric- versus allosteric-dependent activation of the GABAA receptor requires numerically distinct subunit level rearrangements.

Publications

Orthosteric- versus allosteric-dependent activation of the GABA<sub>A</sub> receptor requires numerically distinct subunit level rearrangements.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets