Figure 8.

The effect of β₂ or δ subunit mutation on the expression of α₆β₂δ receptors A, the GABA concentration–response relationship for α₆β^Y157Fδ receptors for three oocytes with 30 nA (•), 70 nA (○) and 180 nA (▾) of spontaneous current. The mutation within the GABA-dependent activation domain (α₆β_Y^157Fδ) did not abolish the spontaneous activity. The continuous lines represent the fit of the GABA data points with a sum of two Hill equations for α₆β^Y157Fδ receptors at different expression levels. The dashed line shows the overall plot of the fit of the GABA concentration–response relationship data with a sum of two Hill equations for the wild-type α₆β₂δ receptor (intermediate expression). The dotted line shows a plot of the fit (group data) of the GABA concentration–response relationship data with a sum of two Hill equations for the α₆β^Y157Fδ receptor. B, the δ^R287M mutation attenuated the spontaneous activity and the GABA maximal current. Top shows the amino acid sequence between the TM2 and TM3 domains of the δ subunit, indicating the position of Arg287. At equivalent expression conditions, the wild-type receptor showed high levels in comparison to no spontaneous activity for α₆β₂δ^R287M receptors (corrected for control leak, see methods). The maximal-induced GABA current for mutated receptor was significantly reduced as compared to that for wild-type receptor.