Figure 1. Co-immunoprecipitation of exogenously expressed β₂AR and D₄DR.

All cells used in these studies transiently co-expressed Gα_s, Gα_i1, Gβ₁, Gγ₂ and AC. In addition they expressed β₂AR and/or the HA-tagged D₄DR. Cells expressing one or the other receptor were mixed prior to preparing membranes (Mixed). So that each sample contained the same ratio of expressed receptor protein to total cell protein, cells co-expressing the receptors (Co-expressed) were mixed with cells receiving plasmid without receptor cDNA. These latter cells (Vector) were also used as a negative control. Membranes prepared from these samples were dissolved in RIPA buffer, and the soluble proteins in the supernatant following centrifugation at 100,000 × g were treated as described in Materials and Methods in order to immunoprecipitate and identify β₂AR and HA-tagged D₄DR on western blots. Data are representative of three independent experiments.