Shisa7-Dependent Regulation of GABA A Receptor Single-Channel Gating Kinetics.

GABA A receptors (GABA A Rs) mediate the majority of fast inhibitory transmission throughout the brain. Although it is widely known that pore-forming subunits critically determine receptor function, it is unclear whether their single-channel properties are modulated by GABA A R-associated transmembrane proteins. We previously identified Shisa7 as a GABA A R auxiliary subunit that modulates the trafficking, pharmacology, and deactivation properties of these receptors. However, whether Shisa7 also regulates GABA A R single-channel properties has yet to be determined. Here, we performed single-channel recordings of α2β3γ2L GABA A Rs cotransfected with Shisa7 in HEK293T cells and found that while Shisa7 does not change channel slope conductance, it reduced the frequency of receptor openings. Importantly, Shisa7 modulates GABA A R gating by decreasing the duration and open probability within bursts. Through kinetic analysis of individual dwell time components, activation modeling, and macroscopic simulations, we demonstrate that Shisa7 accelerates GABA A R deactivation by governing the time spent between close and open states during gating. Together, our data provide a mechanistic basis for how Shisa7 controls GABA A R gating and reveal for the first time that GABA A R single-channel properties can be modulated by an auxiliary subunit. These findings shed light on processes that shape the temporal dynamics of GABAergic transmission. SIGNIFICANCE STATEMENT Although GABA A receptor (GABA A R) single-channel properties are largely determined by pore-forming subunits, it remains unknown whether they are also controlled by GABA A R-associated transmembrane proteins. Here, we show that Shisa7, a recently identified GABA A R auxiliary subunit, modulates GABA A R activation by altering single-channel burst kinetics. These results reveal that Shisa7 primarily decreases the duration and open probability of receptor burst activity during gating, leading to accelerated GABA A R deactivation. These experiments are the first to assess the gating properties of GABA A Rs in the presence of an auxiliary subunit and provides a kinetic basis for how Shisa7 modifies temporal attributes of GABAergic transmission at the single-channel level.