Effect of σ₁ receptor ligands on σ₁-D₂ receptor heteromer.

BRET was measured in HEK-293T cells cotransfected with: (a) D₂–Rluc cDNA (0.4 µg) and increasing amounts of σ₁-YFP receptor cDNA (0.1 to 1 µg), (b) σ₁–Rluc cDNA (0.2 µg) and increasing amounts of σ₁-YFP receptor cDNA (0.1 to 1 µg), (c) D₂–Rluc cDNA (0.4 µg) and increasing amounts of D₂-YFP receptor cDNA (0.2 to 2 µg) or (d) siRNA corresponding to σ₁ receptor (see Methods), D₂–Rluc cDNA (0.4 µg) and increasing amounts of D₂-YFP receptor cDNA (0.2 to 2 µg), not treated (black), treated for 30 min with 30 µM cocaine (red), treated for 10 min with 100 nM PRE084 (blue) or 1 µM PD144418 (green) or treated for 30 min with 30 µM cocaine and 1 µM PD144418 (orange). The relative amount of BRET acceptor is given as the ratio between the fluorescence of the acceptor minus the fluorescence detected in cells only expressing the donor, and the luciferase activity of the donor (YFP/Rluc). BRET data are expressed as means ± SD of four to six different experiments grouped as a function of the amount of BRET acceptor.