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?1-Containing GABA-A Receptors Cluster at Synapses Where they Mediate Slower Synaptic Currents than ?2-Containing GABA-A Receptors.

ABSTRACT: GABA-A receptors (GABAARs) are pentameric ligand-gated ion channels that are assembled mainly from ? (?1-6), ? (?1-3) and ? (?1-3) subunits. Although GABAARs containing ?2L subunits mediate most of the inhibitory neurotransmission in the brain, significant expression of ?1 subunits is seen in the amygdala, pallidum and substantia nigra. However, the location and function of ?1-containing GABAARs in these regions remains unclear. In "artificial" synapses, where the subunit composition of postsynaptic receptors is specifically controlled, ?1 incorporation slows the synaptic current decay rate without affecting channel deactivation, suggesting that ?1-containing receptors are not clustered and therefore activated by diffuse neurotransmitter. However, we show that ?1-containing receptors are localized at neuronal synapses and form clusters in both synaptic and extrasynaptic regions. In addition, they exhibit rapid membrane diffusion and a higher frequency of exchange between synaptic and perisynaptic populations compared to ?2L-containing GABAARs. A point mutation in the large intracellular domain and a pharmacological analysis reveal that when a single non-conserved ?2L residue is mutated to its ?1 counterpart (T349L), the synaptic current decay is slowed from ?2L- to ?1-like without changing the clustering or diffusion properties of the receptors. In addition, previous fast perfusion and single channel kinetic experiments revealed no difference in the intrinsic closing rates of ?2L- and ?1-containing receptors when expressed in HEK293 cells. These observations together with Monte Carlo simulations of synaptic function confirm that decreased clustering does not control ?1-containing GABAAR kinetics. Rather, they suggest that ?1- and ?2L-containing receptors exhibit differential synaptic current decay rates due to differential gating dynamics when localized at the synapse.

SUBMITTER: Dixon CL

PROVIDER: S-EPMC5462899 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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γ1-Containing GABA-A Receptors Cluster at Synapses Where they Mediate Slower Synaptic Currents than γ2-Containing GABA-A Receptors.

Dixon Christine L CL Sah Pankaj P Keramidas Angelo A Lynch Joseph W JW Durisic Nela N

Frontiers in molecular neuroscience 20170608

GABA-A receptors (GABAARs) are pentameric ligand-gated ion channels that are assembled mainly from α (α1-6), β (β1-3) and γ (γ1-3) subunits. Although GABAARs containing γ2L subunits mediate most of the inhibitory neurotransmission in the brain, significant expression of γ1 subunits is seen in the amygdala, pallidum and substantia nigra. However, the location and function of γ1-containing GABAARs in these regions remains unclear. In "artificial" synapses, where th ...[more]

PMID: 28642681

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Project description:GABA is a principal neurotransmitter in the hypothalamic suprachiasmatic nucleus (SCN) that contributes to intercellular communication between individual circadian oscillators within the SCN network and the stability and precision of the circadian rhythms. GABA transporters (GAT) regulate the extracellular GABA concentration and modulate GABAA receptor (GABAAR)-mediated currents. GABA transport inhibitors were applied to study how GABAAR-mediated currents depend on the expression and function of GAT. Nipecotic acid inhibits GABA transport and induced an inward tonic current in concentration-dependent manner during whole cell patch-clamp recordings from SCN neurons. Application of either the selective GABA transporter 1 (GAT1) inhibitors NNC-711 or SKF-89976A, or the GABA transporter 3 (GAT3) inhibitor SNAP-5114, produced only small changes of the baseline current. Coapplication of GAT1 and GAT3 inhibitors induced a significant GABAAR-mediated tonic current that was blocked by gabazine. GAT inhibitors decreased the amplitude and decay time constant and increased the rise time of spontaneous GABAAR-mediated postsynaptic currents. However, inhibition of GAT did not alter the expression of either GAT1 or GAT3 in the hypothalamus. Thus GAT1 and GAT3 functionally complement each other to regulate the extracellular GABA concentration and GABAAR-mediated synaptic and tonic currents in the SCN. Coapplication of SKF-89976A and SNAP-5114 (50 µM each) significantly reduced the circadian period of Per1 expression in the SCN by 1.4 h. Our studies demonstrate that GAT are important regulators of GABAAR-mediated currents and the circadian clock in the SCN.NEW & NOTEWORTHY In the suprachiasmatic nucleus (SCN), the GABA transporters GAT1 and GAT3 are expressed in astrocytes. Inhibition of these GABA transporters increased a tonic GABA current and reduced the circadian period of Per1 expression in SCN neurons. GAT1 and GAT3 showed functional cooperativity: inhibition of one GAT increased the activity but not the expression of the other. Our data demonstrate that GABA transporters are important regulators of GABAA receptor-mediated currents and the circadian clock.

Dataset Information

?1-Containing GABA-A Receptors Cluster at Synapses Where they Mediate Slower Synaptic Currents than ?2-Containing GABA-A Receptors.

Publications

γ1-Containing GABA-A Receptors Cluster at Synapses Where they Mediate Slower Synaptic Currents than γ2-Containing GABA-A Receptors.

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