A Lysine Residue in the β3 Subunit Contributes to the Regulation of GABA A Receptor Activity by Voltage

Abstract

GABA A receptors (GABARs) are responsible for most fast inhibitory neurotransmission in the mammalian brain. The whole-cell currents of many native and recombinant GABARs exhibit outward rectification. This property has been shown to depend in part upon the identity of the α and β subtype, but the structural determinants controlling this characteristic are not well known. An extracellular lysine residue conserved in the β subunit family and located near the third transmembrane domain was examined. Mutations were made in the α1, β3, and γ2L subunits, exchanging the wild-type residue for either the lysine found in the β subunit family or the threonine found in the α and γ families. GABARs containing the mutated α1 or γ2L subunits showed a large increase in outward rectification. Conversely, replacing the lysine in the β3 subunit with threonine resulted in a nearly linear current–voltage relationship and an increased sensitivity to GABA. Replacing this lysine with uncharged or negatively charged residues consistently eliminated outward rectification, with varying effects on GABA sensitivity. Similar mutations of the four other charged residues within the β3 subunit M2-M3 domain did not alter rectification. These results suggest that lysine279 of the β3 subunit plays an important role in the regulation of GABAR activity by membrane voltage.