Fig. 8. The effects of varying protein expression levels on BRET between AC-RLuc and GFP-G₂. HEK 293 cells were transfected with recombinant plasmids to express ß₂AR, G_s and Gß_1, GFP-G₂ and AC-RLuc as described in the Materials and Methods so that the ratio of expressed GFP-G₂ to AC-RLuc remained constant whereas the amounts of these proteins varied over nearly two orders of magnitude (inset). Cells were left untreated (basal) or were exposed to 1 µM isoproterenol before assaying BRET in the presence of 5 µM coelenterazine H using 480 and 450-458 nm filters.