Fig. 7. BRET between tagged effectors and G subunits is agonist-independent. HEK 293 cells were transfected to express the indicated proteins and were stimulated or not with 1 µM isoproterenol. (A) BRET was observed in cells co-expressing AC-RLuc and G_s-GFP though it was not affected by agonist stimulation, and was comparatively less than BRET between AC-RLuc and GFP-G₂. (B) BRET was also observed in cells stably expressing the ß₂AR and co-expressing G_i-RLuc, Gß₁, G₂ and Kir3.1-GFP. BRET was not affected by agonist regardless of whether or not Kir3.4 was co-expressed. The data represent the mean ± s.d. for at least three experiments.