TY - JOUR T1 - D<sub>1</sub>-D<sub>2</sub> Dopamine Receptor Synergy Promotes Calcium Signaling via Multiple Mechanisms JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.113.085175 SP - mol.113.085175 AU - Lani S. Chun AU - R. Benjamin Free AU - Trevor B. Doyle AU - Xi-Ping Huang AU - Michele L. Rankin AU - David R. Sibley Y1 - 2013/01/01 UR - http://molpharm.aspetjournals.org/content/early/2013/05/16/mol.113.085175.abstract N2 - The D1 dopamine receptor (D1R) has been proposed to form a hetero-oligomer with the D2 dopamine receptor (D2R), which in turn results in a complex that couples to PLC-mediated intracellular calcium release. We have sought to elucidate the pharmacology and mechanism of action of this putative signaling pathway. Dopamine dose response curves assaying intracellular calcium mobilization in cells heterologously expressing the D1 and D2 subtypes either alone or in combination, and employing subtype selective ligands, revealed that concurrent stimulation is required for coupling. Surprisingly, characterization of a putative D1-D2 heteromer-selective ligand, SKF83959, found no stimulation of calcium release, but a broad range of cross-reactivity with other GPCRs. In contrast, SKF83959 appeared to be an antagonist of calcium mobilization. Over-expression of Gqα with the D1 and D2 DARs enhanced the dopamine-stimulated calcium response. However, this was also observed in cells expressing Gqα with only the D1R. Inactivation of Gi or Gs with pertussis or cholera toxin, respectively, was found to largely, but not entirely reduce the calcium response in D1R and D2R co-transfected cells. Moreover, we found that sequestration of Gβγ subunits through over-expression of GRK2 mutants either completely or largely eliminated dopamine-stimulated calcium mobilization. Our data suggests that the mechanism of D1R-D2R-mediated calcium signaling involves more than receptor-mediated Gq protein activation, may largely involve downstream signaling pathways, and may not be completely heteromer-specific. In addition SKF83959 may not exhibit selective activation of D1-D2 heteromers, and its significant cross-reactivity to other receptors warrants careful interpretation of its use in vivo. ER -