A48: Activation of the β3 Homomeric GABAA Receptor by Protonation 

Presenter(s)

Saumith Menon

Abstract or Description

GABA_A receptors are pentameric ligand-gated ion channels that are activated by the neurotransmitter GABA. Activation of the receptor causes a conformational change in the receptor that opens the channel gate, admitting chloride ions across the cell membrane, into the cell, producing neuronal inhibition. In addition to GABA, endogenous agents such as neurosteroids, as well as certain clinically employed sedatives, anesthetics, and anxiolytics, can also activate GABA_A receptors. One variant of the GABA_A receptor, known as the β₃ homopentameric GABA_A receptor, was the focus of our study. 

This study’s purpose was to determine the effects of extracellular H+ levels on β₃ homomeric GABA_A receptor activation. A two-electrode voltage clamp setup was used to record ionic currents and assess the functional activity of β₃ GABA_A receptors expressed in Xenopus laevis oocytes at various pH levels. To isolate receptor activation from changes in electrochemical driving force, we employed conductance-based measurements to accurately analyze receptor behavior. We also analyzed the β₃ (H267A) mutant, where the histidine, a basic amino acid, at position 267 was replaced with the non-polar amino acid alanine to determine its contribution to pH sensitivity.

Our results indicate that acidic conditions increase β₃ receptor activation relative to more basic extracellular conditions. On the other hand, the H267A mutation strongly decreased H+-mediated activation, suggesting that histidine protonation plays a key role in the pH sensitivity of the wild-type receptor. Ultimately, this study shows that extracellular protonation influences β₃ homomeric GABA_A receptor activation, with histidine 267 serving as a critical site.