Table 2

Ligand affinity of dopamine D2 receptor in M2, A7, and CHO cells

Dopamine8,900 ± 2,63010,100 ± 4,9705,330 ± 2,020
Dopamine + GTP2-150 25,17526,455ND
6,7-ADTN350 ± 70330 ± 120ND
(−)-Sulpiride170 ± 40160 ± 10ND
Haloperidol3.16 ± 0.292.41 ± 0.471.80 ± 0.60

K i values (nM) were calculated from [3H]spiperone (0.1–0.3 nM) competition binding of agonists and antagonists on D2 stably expressed M2 (ABP-280-deficient), A7 (genetically reconstituted ABP-280), and CHO cells. Curves were fitted as one-site competition binding. Data shown are the mean ± S.E. of three independent experiments, assayed in duplicate. D2 receptor expression levels were 2.48 pmol/mg of protein (M2) versus 2.55 pmol/mg of protein (A7). The stable CHO cell clone used contained receptor levels of 1.07 pmol/mg of protein. No significant change in either agonist or antagonist affinity for D2 receptors was observed in M2, A7, or CHO cells.

    • 2-150 GTP concentration was 50 μM; K i was calculated as the average of two experiments.

    • ND, not determined.