Labeling of dopamine D-3 and D-4 receptor subtypes in human peripheral blood lymphocytes with [H-3]7-OH-DPAT: a combined radioligand binding assay and immunochemical study

Molecular biology studies have demonstrated that human peripheral blood lym phocytes express dopamine D-2-like receptors belonging to the D-3 and D-4 r eceptor subtypes, whereas the characterization of these receptors using rad ioligand binding assay techniques provided conflicting results. The prefere ntial dopamine D-3 receptor agonist [H-3]7-hydroxy-N,N-di-n-propyl-2-aminot etralin ([H-3]7-OH-DPAT) was used recently for labeling lymphocyte dopamine D-3 receptor. However, the selectivity of this compound for the D, recepto r was questioned. In this study we have investigated human peripheral blood lymphocyte dopamine receptor subtypes labeled by [H-3]7-OH-DPAT using a co nventional radioligand binding assay technique and antibodies against dopam ine D-2-like receptor subtypes. [H-3]7-OH-DPAT was specifically bound to in tact human peripheral blood lymphocytes with a dissociation constant (K-d) value of 0.32 + 0.03 nM and a maximum density of binding sites (B-max) of 1 8.2 + 0.8 fmol/2 x 10(6) cells. [H-3]7-OH-DPAT binding was unaffected by an tibodies against dopamine D-2 and D-2S receptors. Anti-dopamine D-3 and D-4 receptor antibodies reduced [H-3]7-OH-DPAT binding by about 53% and 32% re spectively. Combination of anti D-3 and D-4 receptor antibodies reduced rem arkably [H-3]7-OH-DPAT binding. The above results suggest that the dopamine receptor agonist [H-3]7-OH-DPAT labels dopamine D-3 and D-4 receptor subty pes in human peripheral blood lymphocytes. The use of antibodies raised aga inst dopamine receptor subtypes in combination with radioligand binding ass ay may contribute to define receptor subtypes expressed by human peripheral blood lymphocytes in health and disease. (C) 1998 Elsevier Science B.V. Al l rights reserved.