Characterization of dopamine D2 receptor gene expression and binding sites in human placenta amniotic epithelial...

This study was to investigate the presence of dopamine (DA) D(2)receptors mRNA and binding sites in human amniotic epithelial cells (HAEC). RT-PCR revealed that HAEC express DA D(2)receptor mRNA that is having 100 per cent homology with human DA D(2)receptors. Radioligand saturation binding studies showed a [3H]YM-09151-2 high affinity binding site with a K(D)and B(max)values of 0.53+/-0.09 nM and 119.6+/-8.5 fmol/mg protein, respectively. Competition experiments demonstrated that selective D(2)antagonists such as spiroperidol, domperidone and eticlopride potently competed with [3H]YM-09151-2 binding, whereas selective D(1)antagonists like SCH 23390 displayed weaker competition for the binding sites. The rank order of potency of these compounds in competing with [3H]YM-09151-2 for the binding sites was consistent with the pharmacology of the DA D(2)receptors. All competition curves were better fitted to a one-site model with a Hill coefficient around unity, indicating that [3H]YM-09151-2 is labelling a single population of receptors. These results provide evidence that HAEC natively express DA D(2)receptor mRNA and binding sites. Although the physiological function of D2 receptors in HAEC is currently unclear, the present results suggest that these cells could represent a source of human DA D(2)receptors without transformation or cloning procedures.