Pharmacological analysis of dopamine stimulation of [S-35]-GTP gamma S binding via human D-2short and D-2long dopamine receptors expressed in recombinant cells

1 The activation of G-proteins by agonist-occupied D-2 or D-3 dopamine receptors in membranes from recombinant cells expressing the cloned receptors has been analysed by a [S-35]-guanosine 5'-[gamma-thio] triphosphate ([S-35]-GTP gamma S) binding assay. 2 The rate of [S-35]-GTP gamma S binding was increased by dopamine in a dose-dependent manner in membranes from CHO cells stably expressing either the D-2short or D-2long dopamine receptor. 3 The dopamine-induced stimulation of [S-35]-GTP gamma S binding could be inhibited by a range of antagonists. Affinities for antagonists derived from the inhibition of the dopamine stimulation of [S-35]- GTP gamma S binding correlated very well with affinities derived from radioligand binding studies. 4 When the maximum [S-35]-GTP gamma S binding responses stimulated by dopamine acting at different receptor subtypes were compared, there was a tendency for the stimulation via the D-2short receptor to be greater than via the D-2long receptor and for the stimulation via the D-3 dopamine receptor to be less than for either D-2 receptor. These differences in maximal response were also seen when the inhibitory effects of dopamine on adenylyl cyclase via the three receptor subtypes were compared. 5 The stimulation of [S-35]-GTP gamma S binding by dopamine in membranes from recombinant cells therefore provides an excellent system for studying the molecular nature of agonism and the receptor/G-protein interactions for these receptors.