Dopamine- and pramipexole-induced
tolerance is not elicited in the D3 D187A mutant receptor. Tolerance
property defined as the ratio of second/first agonist-induced GIRK
response was determined for dopamine (100 nM), ES609 (100 nM), cis-8-OH-PBZI
(300 nM), pramipexole (300 nM), 7-OH-DPAT (100 nM), and 7-OH-PIPAT
(100 nM) in AtT-20 cells transiently transfected with either wild
type D3 (black fill) or D3 D187A mutant (cross hatched) receptors.
The tolerance induced by dopamine and pramipexole in wild type D3
receptor is significantly attenuated in the D3 D187A mutant receptors;
*P < 0.01, ANOVA (Holm’s-Sidak post hoc
test). The bars represent the mean values ± SEM (n = 5–8 cells).