Figure 2.

Functional expression of WT and L9′S mutant α4, β3 and δ subunits. In this and subsequent figures, WT α4, β3 and δ subunits are labelled as α, β and δ, whereas mutated α4(L297S), β3(L284S) and δ(L288S) subunits are designated as α_m, β_m and δ_m. (A) Examples of whole-cell currents elicited by increasing concentrations of GABA on HEK cells expressing recombinant αβδ, αβδ_m, α_mβδ and αβ_mδ receptors. A transfection ratio of 10α:1β:10δ was used. Note the increased GABA sensitivity and prolonged deactivation kinetics exhibited by mutant-expressing cells. (B) Bar graph of SA for αβδ, αβδ_m, α_mβδ, αβ_mδ and α_mβδ_m receptors. Values were calculated by expressing the outward current induced by the Cl⁻ channel blocker picrotoxin (I_PTX; 1 mM) as a percentage of the maximum current, defined as the sum of I_Max,GABA and I_PTX (n = 4–11; mean ± SEM). No SA (= 0%) was observed for WT α4β3δ receptors. The inset shows example GABA-activated and picrotoxin-sensitive currents (I_Max,_GABA and I_PTX) for αβδ and αβδ_m receptors. Current calibration bars: 300 pA (αβδ); 400 pA (αβδ_m).