Table 2.

Binding of drugs to D₂ dopamine receptors

	+Na+	+Na++GTP	+NMDG	+NMDG +GTP
AJ-76	6.54±0.03	6.50±0.01	5.45±0.07*	5.20±0.03*
Aplindore	pKh 10.22±0.29		pKh 9.80±0.14
	pKl 9.08±0.16	9.03±0.09	pKl 8.45±0.07*	8.40±0.06*
	%Rh 15.22±7.8		%Rh 52.6±3.5
Aripiprazole	9.03±0.12	8.96±0.14	8.80±0.13	8.56±0.13
Dopamine	pKh 7.10±0.20		pKh 7.73±0.19	5.38±0.14 (3)
	pKl 5.40±0.09	5.28±0.07	pKl 5.68±0.16
	%Rh 42.4±3.1		%Rh 49.5±5.5
				pKh 6.48±0.13
				pKl 5.02±0.12**
				%Rh 54.4±3.0 (4)
(−)-3-PPP			pKh 7.34±0.13
	6.47±0.08	6.23±0.07	pKl 5.77±0.16*	5.63±0.16*
			%Rh 51.9±4.3
UH-232	7.23±0.06	7.14±0.06	6.62±0.07*	6.03±0.05*,**

Abbreviations: AJ-76, (1S,2R)-cis-5-methoxy-1-methyl-2-(N-propylamino)tetralin; CHO, Chinese hamster ovary; GTP, guanine 5′-triphosphate; NMDG, N-methyl D-glucamine.

The binding of drugs to D₂ dopamine receptors in membranes of CHO cells expressing the D₂ receptor was determined in competition versus [³H]spiperone binding as described in the Materials and methods. Experiments were performed under four different conditions: in the presence of Na⁺ (100 mM) or NMDG (100 mM), with and without GTP (100 μM). Data were fitted to one- and two-binding site models and the best-fit data are given (pK_i for a one-binding site fit and pK_h, pK_l and %R_h for a two-binding site fit, for dopamine (+NMDG, +GTP) three experiments were fitted best by a one-binding site model and four by a two-binding site model). Data are given as mean±s.e.m. from at least three experiments.

^*P<0.05 for effect of Na⁺

^**P<0.05 for effect of GTP.