Labelling of D2-dopaminergic and 5-HT2-serotonergic binding sites in human trophoblastic cells using [3H]-spiperone.
We previously reported that dopamine (DA) inhibited the release of human placental lactogen (hPL) from human placental cells. We also demonstrated the presence of D2-dopamine receptors in membrane preparations of human term placenta. The aim of the present study was to characterize these D2 receptors on freshly isolated human trophoblastic cells. The binding of [3H]-spiperone to these cells showed a curvilinear Scatchard plot suggesting the presence of two classes of binding sites (Kd1 = 1.26nM; Kd2 = 44.3nM). Competition experiments showed the following inhibitory binding potencies: serotonin-2 (5-HT2) > or = D2 >>> alpha-adrenergic, beta-adrenergic, D1-dopamine, thus suggesting the presence of 5-HT2 binding sites. We have examined this possibility by blocking [3H]-spiperone binding to 5-HT2 receptors in the presence of 50nM ketanserin, a selective antagonist of 5-HT2 sites. Under this condition, the linear Scatchard plot obtained suggested a single population of homogeneous binding sites for [3H]-spiperone with a Kd of 0.55nM. To further characterize placental D2 receptors we conducted binding experiments with [3H]-raclopride, an more selective D2 antagonist. The linear Scatchard plot obtained with this ligand suggested one class of binding sites for [3H]-raclopride (Kd = 6nM) with the following inhibitory potencies: D2 >>> beta-adrenergic >> 5-HT2, D1, alpha-adrenergic. These results suggest an important paracrine function for DA in human placenta and show for the first time that [3H]-spiperone binds putative 5-HT2 receptors in human placenta.
Vaillancourt
C
C
Departement of Obstetrics and Gynecology, Faculty of Medecine, University of Montreal, Quebec, Canada.
Petit
A
A
Gallo-Payet
N
N
Bellabarba
D
D
Lehoux
J G
JG
Bélisle
S
S
D006801:Humans; D066298:In Vitro Techniques; D011869:Radioligand Assay; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000378:metabolism*; D013134:Spiperone / Q000378:metabolism*; D014316:Tritium; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism*
D017448:Receptors, Dopamine D2; D011985:Receptors, Serotonin; D014316:Tritium; D013134:Spiperone