Table 4. Efficacy of NE, DA, clonidine, 7-OH-PIPAT and quinpirole obtained from G protein activation experiments mediated by α_2A and α_2C adrenoceptors coupled to the different Gαi/o subtypes.

Gα Subunit	Receptor	NE	DA	Clonidine	7-OH-PIPAT	Quinpirole
Gαi1	α2A	100 ± 5	120 ± 6 *	120 ± 5	94 ± 6	70 ± 2 *
	α2C	100 ± 2	105 ± 5	64 ± 4 **	41 ± 1 **	ND
Gαi2	α2A	100 ± 10	120 ± 20	89 ± 6	55 ± 2 *	47 ± 8 *
	α2C	100 ± 7	80 ± 10	107 ± 4	90 ± 20	46 ± 9 **
Gαi3	α2A	100 ± 10	90 ± 10	112 ± 8	71 ± 6	40 ± 9 **
	α2C	100 ± 9	95 ± 6	85 ± 5	90 ± 10	80 ± 15
Gαo1	α2A	100 ± 7	108 ± 6	110 ± 10	81 ± 9	78 ± 9
	α2C	100 ± 10	100 ± 10	41 ± 3 **	98 ± 7	42 ± 3 **
Gαo2	α2A	100 ± 9	110 ± 10	120 ± 2	85 ± 4	72 ± 8
	α2C	100 ± 8	114 ± 6	70 ± 8 *	106 ± 3	34 ± 6 **

Efficacy (E_max values, as percentage of NE values) of NE, DA, clonidine and D₂-like receptor ligands obtained from G protein activation experiments mediated by α_2A and α_2C coupled to the different Gαi/o subtypes (Figures 3 and 4). E_max values were obtained from a sigmoidal concentration-response function adjusted by nonlinear regression analysis and are expressed as means ± S.E.M. of 3 to 11 experiments performed in triplicate. In italics, values of E_max lower than 50%. ND: not detectable. Statistical differences between NE and the other ligands for each receptor and Gαi/o protein subtype were calculated by one-way ANOVA, followed by Dunnett post hoc test;

^*p<0.05,

^**p<0.01 and

^***p <0.001.