Fluorescence studies reveal heterodimerization of dopamine D1 and D2 receptors in the plasma membrane

Evidence for hetero-oligomerization has recently been provided for various G protein-coupled receptors. In this paper, we have studied the possibility that dopamine D-1 and D-2 receptors physically interact with each other. Human dopamine D1 and D2 receptors were fluorescently tagged with derivatives of green fluorescence protein and transiently coexpressed in the membrane of human embryonic kidney 293 cells. Using qualitative fluorescence spectroscopy, as well as quantitative Forster resonance energy transfer (FRET) analysis, performed in a single cell by confocal microscopy and fluorescence lifetime microscopy, we show that dopamine D-1 and D-2 receptors can form hetero-oligomers in the plasma membrane. The degree of receptor protein-protein interaction is significantly enhanced by concomitant addition of D1 and D2 receptor subtype-specific agonists. Our investigations extend biochemical and electrophysiological studies and give insights into the regulation and synergistic mode of operation of dopamine receptors.