Figure 1.

Agonist-stimulated [³⁵S]GTPγS dissociation from membranes of CHO cells expressing D₂ dopamine receptors. Membranes were incubated with [³⁵S]GTPγS (0.2 nM) for 60 min as described in the Materials and methods section. 1 mM dopamine, 1 mM m-tyramine, 1 mM p-tyramine or vehicle were then added to the assays, together with 10 μM GTPγS and the [³⁵S]GTPγS dissociation determined. Data were fitted best by a model of a single exponential decay. t_1/2 values obtained were 2.3±0.2 min for dopamine, 3.6±0.6 min for m-tyramine, 4.5±0.1 min for p-tyramine and 6.5±1.1 min for basal. Maximal [³⁵S]GTPγS dissociated was 63.0±2.6% for dopamine, 62.2±1.8% for m-tyramine, 55.7±1.0% for p-tyramine and 51.1±1.7% for basal. This graph shows the data from a single representative experiment carried out three times with similar results.