Conductance of recombinant GABA_A channels is increased in cells co-expressing GABA_A receptor-associated protein

High conductance γ-aminobutyric acid type A (GABA_A) channels (>40 picosiemens (pS)) have been reported in some studies on GABA_A channels in situ but not in others, whereas recombinant GABA_A channels do not appear to display conductances above 40 pS. Furthermore, the conductance of some native GABA_A channels can be increased by diazepam or pentobarbital, which are effects not reported for expressed GABA_A channels. GABARAP, a protein associated with native GABA_A channels, has been reported to cause clustering of GABA _A receptors and changes in channel kinetics. We have recorded single channel currents activated by GABA in L929 cells expressing α ₁, β₁, and γ_2S subunits of human GABA_A receptors. Channel conductance was never higher than 40 pS and was not significantly increased by diazepam or pentobarbital, although open probability was increased. In contrast, in cells expressing the same three subunits together with GABARAP, channel conductance could be significantly higher than 40 pS, and channel conductance was increased by diazepam and pentobarbital. GABARAP caused clustering of receptors in L929 cells, and we suggest that there may be interactions between subunits of clustered GABA _A receptors that make them open co-operatively to give high conductance "channels." Recombinant channels may require the influence of GABARAP and perhaps other intracellular proteins to adopt a fuller repertoire of properties of native channels.