GABAA Receptor α and γ Subunits Shape Synaptic Currents via Different Mechanisms

Background: GABA(A)R 2 and 1 subunits are highly expressed in amygdala but their influence on synaptic currents is unknown. Results: 2 subunits increased GABA affinity thereby slowing current deactivation; 1 subunits reduced synaptic receptor clustering. Conclusion: These subunits may differentially shape synaptic kinetics. Significance: Understanding how 2 and 1 subunits shape synaptic currents may help us understand amygdala processing mechanisms. Synaptic GABA(A) receptors (GABA(A)Rs) mediate most of the inhibitory neurotransmission in the brain. The majority of these receptors are comprised of 1, 2, and 2 subunits. The amygdala, a structure involved in processing emotional stimuli, expresses 2 and 1 subunits at high levels. The effect of these subunits on GABA(A)R-mediated synaptic transmission is not known. Understanding the influence of these subunits on GABA(A)R-mediated synaptic currents may help in identifying the roles and locations of amygdala synapses that contain these subunits. Here, we describe the biophysical and synaptic properties of pure populations of 122, 222, 121 and 221 GABA(A)Rs. Their synaptic properties were examined in engineered synapses, whereas their kinetic properties were studied using rapid agonist application, and single channel recordings. All macropatch currents activated rapidly (<1 ms) and deactivated as a function of the -subunit, with 2-containing GABA(A)Rs consistently deactivating approximate to 10-fold more slowly. Single channel analysis revealed that the slower current decay of 2-containing GABA(A)Rs was due to longer burst durations at low GABA concentrations, corresponding to a approximate to 4-fold higher affinity for GABA. Synaptic currents revealed a different pattern of activation and deactivation to that of macropatch data. The inclusion of 2 and 1 subunits slowed both the activation and deactivation rates, suggesting that receptors containing these subunits cluster more diffusely at synapses. Switching the intracellular domains of the 2 and 1 subunits substantiated this inference. Because this region determines post-synaptic localization, we hypothesize that GABA(A)Rs containing 1 and 2 use different mechanisms for synaptic clustering.