RT Journal Article
SR Electronic
T1 Comparison of the Ligand Binding and Signaling Properties of Human Dopamine D<sub>2</sub> and D<sub>3</sub> Receptors in Chinese Hamster Ovary Cells
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 908
OP 916
VO 290
IS 2
A1 Jurgen F. M. Vanhauwe
A1 Norbert Fraeyman
A1 Bart J. B. Francken
A1 Walter H. M. L. Luyten
A1 Josée E. Leysen
YR 1999
UL http://jpet.aspetjournals.org/content/290/2/908.abstract
AB Human dopamine D2 (hD2) and D3 (hD3) receptors were expressed at similar, high expression levels in Chinese hamster ovary (CHO) cells, and their coupling to G proteins and further signal transduction pathways were compared. In competition radioligand-binding experiments, guanosine-5′-O-(3-thio)triphosphate (GTPγS) treatment of hD2S- or hD3-CHO cell membranes induced a rightward shift and steeping of the dopamine inhibition curve. This effect was pronounced for hD2 receptors and small for hD3 receptors. Activation of G proteins was investigated in [35S]GTPγS-binding assays. Dopamine stimulated [35S]GTPγS binding 330 and 70% over basal levels on hD2-CHO and hD3-CHO cell membranes, respectively. (+)-7-(Dipropylamino)-5,6,7,8-tetrahydro-2-naphthalenol and PD128907 were partial agonists for both receptors. Haloperidol, risperidone, raclopride, and nemonapride inhibited dopamine-stimulated [35S]GTPγS binding with potencies comparable to their binding affinities for hD2 and hD3 receptors in CHO cell membranes; inverse agonism could not be detected with this assay. Receptor stimulation by dopamine inhibited forskolin-induced cyclic AMP formation in hD2-CHO and hD3-CHO cells by 70%. Furthermore, the extracellular acidification rate increased when hD2-CHO and hD3-CHO cells were stimulated by dopamine; this effect was abolished by pertussis toxin pretreatment. In this study, we could demonstrate clear functional effects at different levels of the signaling cascade of hD2and hD3 receptors in CHO cells when expressed at high levels. High-affinity agonist binding to hD2 and hD3 receptors was still present, but effects of receptor-G protein uncoupling at hD3 receptors were small, indicating that hD3 receptors maintain relatively high-affinity agonist binding in the absence of G proteins. The American Society for Pharmacology and Experimental Therapeutics