Table 2.

Pharmacological parameters of the concentration–response curves of [³⁵S]GTPγS binding stimulation induced by different agonists in absence and presence of selective antagonists in human caudate

	log EC50H	log EC50L	Emax (%)	Fraction H (%)
Dopamine	− 5.25 ± 0.10	–	29 ± 1	N/A
Dopamine + haloperidol	− 4.01 ± 0.19	–	12 ± 1a	N/A
Dopamine + SCH23390	− 4.85 ± 0.17	–	30 ± 2	N/A
SKF38393	− 5.46 ± 0.23	–	14 ± 1	N/A
SKF38393 + SCH23390	− 5.63 ± 0.33	–	12 ± 1	N/A
N-propylapomorphine (NPA)	− 8.10 ± 0.28	− 4.93 ± 0.23	38 ± 4	56 ± 11
NPA + haloperidol	–	− 5.25 ± 0.14	25 ± 2	N/A
NPA + SCH23390	− 7.39 ± 0.26	–	21 ± 1	N/A
NPA + MDL11939	− 8.03 ± 0.21	− 4.76 ± 0.30	37 ± 3	54 ± 8

Values are means ± SE of independent experiments performed in tissue homogenates from 4–7 different control subjects. logEC₅₀ values are log normalized values of the agonist concentration that elicited half-maximal effect obtained from concentration–response curves. E_max is the maximal % stimulation of [³⁵S]GTPγS binding over basal values. H and L represents the high-, and low-affinity fractions of the curves, respectively. N/A: not applicable due to the existence of a monophasic curve model. ^aE_max for dopamine + haloperidol represents an approximate estimation due to absence of asymptotic values