FIGURE 5.

Characterization of quinpirole-induced recruitment of arrestin3. A, time course of mVenus-Arr3 recruitment to D₂-WT-Rluc8 and D₂-A3-Rluc8 receptors during treatment with quinpirole (1 μm). Each point represents the mean ± S.E. (error bars) of four independent experiments. Also depicted in the figure is the ratio of the responses mediated by D₂-A3 and D₂-WT (A3/WT) at each time point. Expression of D₂-WT-Rluc8 was 964 ± 569 fmol/mg protein, and expression of D₂-A3-Rluc8 was 730 ± 143 fmol/mg protein. B, inhibition of the quinpirole-induced recruitment of arrestin3 by the antagonist sulpiride. HEK293 cells expressing D₂-WT-Rluc8 or D₂-A3-Rluc8 with mVenus-Arr3 were pretreated with (S)-(−)-sulpiride at the indicated concentrations for 15 min at room temperature before the addition of quinpirole (10 μm, 10 min). Results are expressed as a percentage of quinpirole-induced BRET for D₂-WT in the absence of sulpiride. Each value represents the mean ± S.E. of four independent experiments. Receptor density and the basal BRET for D₂-WT-Rluc8 were 733 ± 41 fmol/mg protein and 0.06 ± 0.005, and the values for D₂-A3-Rluc8 were 698 ± 87 fmol/mg protein and 0.12 ± 0.007.