Functional expression and characterization of human D2 and D3 dopamine receptors.
Functional characteristics of human D2 and D3 receptors (DRs) were examined using a new bioassay suited for the study of Gi-protein-coupled receptors (GiRs). The bioassay utilizes pigment granule aggregation within cultured Xenopus laevis melanophores for the quantitative evaluation of ligands as agonists or antagonists upon particular GiRs. Initial feasibility studies were performed by analyzing a melanocyte receptor endogenous to the melanophores. In dose-dependent manners, melatonin inhibited melatonin-stimulating hormone-induced cAMP accumulation and caused pigment aggregation that could be monitored over time. Next, melanophores were transiently transfected with cDNAs coding for the human D2BR (short form) and D3R. Expression of either receptor conferred upon the cells the ability to aggregate their melanosomes in response to selective dopaminergic agonists. The same ligands also inhibited cAMP accumulation within the transfected melanophores, and the agonist-induced pigment aggregation was shown to be sensitive to pertussis toxin. EC50 and IC50 value determinations revealed that agonists activated the D2R and D3R at similar concentrations, while each of the antagonists displaying an effect was more potent upon the D2R. The results reveal functional similarities and differences between the D2R and D3R.
Potenza
M N
MN
Department of Cell Biology, Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.
Graminski
G F
GF
Schmauss
C
C
Lerner
M R
MR
D000818:Animals; D001681:Biological Assay; D000242:Cyclic AMP / Q000378:metabolism; D015259:Dopamine Agents / Q000494:pharmacology; D018492:Dopamine Antagonists; D006801:Humans; D008024:Ligands; D009074:Melanocyte-Stimulating Hormones / Q000494:pharmacology; D008547:Melanophores / Q000378:metabolism; D008550:Melatonin / Q000494:pharmacology; D037342:Pertussis Toxin; D010860:Pigments, Biological; D011954:Receptors, Dopamine / Q000378:metabolism*; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D050637:Receptors, Dopamine D3; D013764:Tetrahydronaphthalenes / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014982:Xenopus laevis
C493593:DRD3 protein, human; D015259:Dopamine Agents; D018492:Dopamine Antagonists; D008024:Ligands; D010860:Pigments, Biological; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D013764:Tetrahydronaphthalenes; D010566:Virulence Factors, Bordetella; D009074:Melanocyte-Stimulating Hormones; D000242:Cyclic AMP; D037342:Pertussis Toxin; D008550:Melatonin; C031349:7-hydroxy-2-N,N-dipropylaminotetralin