Radioligand binding characterization of putative dopamine D3 receptor in human peripheral blood lymphocytes with [3H]7-OH-DPAT.

The presence and the pharmacological profile of dopamine D3 receptor have been investigated in human peripheral blood lymphocytes using radioligand binding techniques and the selective dopamine D3 receptor agonist [3H]7-hydroxy-N,N-di-n-pro-pyl-2-aminotetralin ([3H]7-OH-DPAT) as a ligand. [3H]7-OH-DPAT binding to human peripheral blood lymphocytes was time-, temperature-, and concentration-dependent and of high affinity with a dissociation constant value (Kd) of 0.27 +/- 0.05 nM and a maximum binding density (Bmax) of 14.7 +/- 0.06 fmol/2 x 10(6) cells. Binding was also reversible. The rank order of potency of displacers of [3H]7-OH-DPAT binding to human peripheral blood lymphocytes resembled that found for dopamine D3 receptor in rat brain homogenates or in rat or human cell lines. Our findings, which are consistent with those of other authors performed with molecular biology techniques, suggest that human peripheral blood lymphocytes express dopamine D3 receptor. In the brain, dopamine D3 receptor probably mediates the anti-psychotic effect of neuroleptics. The availability of a rapid and reproducible technique for its assay may contribute to evaluate its status in brain disorders characterized by impaired dopaminergic neurotransmission.