To assess the role of the α2, β2 and γ3 subunits in forming functional GABAA receptors we compared the amplitudes and characteristics of GABA induced currents produced in oocytes injected with a 1:1 ratio of α2:β2 mRNAs to oocytes injected with a 1:1:1 ratio of α2:β2:γ3 mRNAs. We routinely tested uninjected oocytes for endogenous GABA currents and no currents were detected under these recording conditions. Injecting α2 mRNA alone (up to 30 ng per oocyte) did not produce detectable currents when tested with up to 100 μM GABA. Functional GABAA receptors were produced by injection of mRNAs for two subunits, α2 and β2, however injecting mRNAs for all three subunits produced significantly greater currents at 10 μM GABA (1.38 ± 0.26 μA (n = 35) vs. 4.30 ± 0.35 μA (n = 31, p < 0.01) (Figure 1A). Currents induced by 1 μM GABA were slightly larger but not significantly so when all 3 subunits were expressed compared to 2 subunits (0.19 ± 0.06 μA (n = 6) vs. 0.47 ± 0.13 μA (n = 8). No differences were evident between injection groups in the rates or degree of desensitization in the GABA-induced inward currents (see inset in Figure 1A).
