GABA_AR isoform and subunit structural motifs determine synaptic and extrasynaptic receptor localisation

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• GABA_A receptors (GABA_ARs) are crucial for inhibitory neurotransmission in the central nervous system.
• Different GABA_AR subtypes mediate synaptic and tonic inhibition, residing in distinct cellular locations.
• Understanding GABA_AR mobility is key to comprehending inhibitory efficacy, yet remains poorly understood.

Purpose of the Study:

• To investigate the mobility and synaptic access of key synaptic and extrasynaptic GABA_AR subtypes.
• To determine how receptor subunit composition and intracellular domains influence GABA_AR diffusion and synaptic retention.

Main Methods:

• Incorporation of silent α-bungarotoxin binding sites (BBS) into GABA_AR subunits.
• Single particle tracking using quantum dots to monitor receptor movement.
• Analysis of diffusion rates and synaptic retention of various GABA_AR isoforms and chimeras.

Main Results:

• All studied GABA_AR isoforms, traditionally considered synaptic or extrasynaptic, can access inhibitory synapses.
• Receptor mobility varies, with α2 and α4 subunits showing longer synaptic residence than α5 and δ subunits.
• Extrasynaptic δ-containing receptors exhibit slower diffusion, which is reversed by a γ2L intracellular domain chimera.
• Receptor activation impacts extrasynaptic GABA_AR diffusion but not synaptic GABA_AR diffusion.

Conclusions:

• Differential mobility profiles of GABA_ARs are governed by subunit composition and intracellular structural motifs.
• These mobility differences are critical determinants of GABA inhibition efficacy.
• The findings shed light on the dynamic regulation of GABAergic signaling in the brain.