Vol. 297, Issue 1, 133-140, April 2001

Dynamic Dopamine-Antagonist Interactions at Recombinant Human Dopamine D_2short Receptor: Dopamine-Bound versus Antagonist-Bound Receptor States

Petrus J. Pauwels, Fréderic Finana, Stéphanie Tardif, Thierry Wurch and Francis C. Colpaert

Department of Cellular and Molecular Biology, Centre de Recherche Pierre Fabre, Castres, France

Antipsychotic drugs comprise a wide range of structurally diverse compounds and are considered to be antagonists at dopamine D₂ receptors. High-resolution kinetic analyses of their antagonist properties was performed by monitoring dynamic dopamine (DA)-antagonist interactions at the recombinant human dopamine D_2short receptor. Time-dependent Ca²⁺ responses were measured following activation of a chimeric G_q/o protein in Chinese hamster ovary-K1 cells. DA (10 µM) induced a rapid, high-magnitude Ca²⁺ response (T_max = 13.2 ± 0.7 s) followed by a low-magnitude phase, which continued throughout the recorded time period (15 min). Of a large series of putative DA antagonists, (+)-UH 232 and bromerguride demonstrated positive, DA-like intrinsic activity at the presumably unoccupied, DA-free receptor; the other antagonists being silent. Antagonists differed in terms of their abilities to prevent the high-magnitude Ca²⁺ phase in the antagonist-bound receptor state, and to reverse the low-magnitude Ca²⁺ phase in the DA-bound state. The benzamide derivatives tropapride and nemonapride fully antagonized both the high- and low-magnitude Ca²⁺ response. Haloperidol, risperidone, and S 14066 also antagonized both responses but with a maximal effect of only 62 to 79%. Although preventing the high-magnitude response (85-95%), the further putative antagonists (+)-butaclamol (6%), bromerguride (27%), and domperidone (41%) reversed the low-magnitude response only weakly and partially. These Ca²⁺ data indicate that putative DA antagonists act differently, in particular, at the DA-bound D_2short receptor.