Table 1

Characterization of D₁ wild-type and mutant receptors

D₁Construct	[³H]SCH-23390 Binding		cAMP Production
D₁Construct	B_max	K_d	V_max	EC₅₀
	pmol/mg of protein	nM	pmol/60,000 cells	μM
Wild-type	0.43 ± 0.03	0.17 ± 0.01	22.2 ± 2.2	0.09 ± 0.014
Mut I	0.47 ± 0.03	0.21 ± 0.03	24.7 ± 3.0	0.05 ± 0.001
Mut II	0.42 ± 0.01	0.25 ± 0.03	27.4 ± 2.3	0.10 ± 0.007
Mut III	0.27 ± 0.04	0.26 ± 0.04	22.9 ± 2.5	0.19 ± 0.015
Mut IV	0.42 ± 0.07	0.23 ± 0.05	28.3 ± 2.9	0.09 ± 0.009
Mut Q	0.40 ± 0.07	0.18 ± 0.01	23.6 ± 3.2	0.12 ± 0.015

The wild-type and mutant D₁ receptor constructs, including the quadruple mutant (Mut Q) and the single point mutants, were stably expressed in C6 glioma cells and examined for their radioligand binding and functional properties as described in Figs. 2 and 3. The data represent mean ± S.E.M. values from three independent experiments.