Stimulating and inhibitory effects of the dopamine "stabilizer" (-)-OSU6162 on dopamine D₂ receptor function in vitro

The effect of (-)-OSU6162 on the incorporation of GTPgammaS³⁵ in the membranes of hD_2l-transfected CHO cells was investigated. In the absence of dopamine the compound exerted a slight but significant stimulating action, suggesting a weak partial agonism. In the presence of dopamine, low concentrations (10 to 100nM) enhanced the stimulating action of dopamine. This enhancing effect was reversed by higher concentrations of (-)-OSU6162 in a complex biphasic manner. The dopamine-enhancing action is proposed to be mediated by binding to an allosteric site with high affinity and the inhibitory component by a low-affinity binding to the orthosteric site of the dopamine receptor.