The distinctive assembly pattern of ε subunit in ternary α1β3ε and binary β3ε GABAA receptors

Abstract

Among all GABAA receptor subunits, ε subunit is a more recent discovery. ε subunit-containing GABAA receptors exhibit spontaneous channel activity, rapid desensitisation, low sensitivity to Zn2+, smaller GABAmediated current amplitudes and an insensitivity to benzodiazepines, despite displaying an agonistic effect at higher benzodiazepine concentrations. The promiscuous role of the ε subunit, co-assembling with other subunits forming GABAARs, may add to the complexities of the pharmacological properties of GABAARs; however, these varying pharmacological responses can be used to distinguish varying subunit combinations of these receptors. Using two electrode voltage-clamped electrophysiology, we investigated the GABAA α1β3ε and β3ε receptors and explored the effects of different stoichiometries of these receptor subtypes by varying the relative ratios of α1/β3/ε (for α1β3ε receptors) and β3/ε (for β3ε receptors) subunit complementary RNA injections into Xenopus laevis oocytes. We discovered the existence of different populations of GABAA α1β3ε and β3ε receptors, due to subunit ratio variation, in which receptors formed at each injection ratio showed different level of GABA sensitivities, spontaneous current activities and Zn2+ mediated current inhibition. These unique pharmacological features are tightly associated with various subtypes of GABAA receptors contributed by the unique assembly pattern of ε subunit.