Pharmacological and internalization properties of delta agonists at the DOR-eGFP receptor (see Materials and Methods).

For competition binding experiments, affinities are shown as Ki values. For the [35S]GTPγS assay, ligand potencies are expressed as EC50 values, and maximum activation levels are indicated as Emax. Basal binding (100%) is defined as [35S]GTPγS responses in absence of ligand. All data are expressed as mean±SEM from 3–4 independent experiments performed in duplicate with two different membrane preparations. ***p<0.001, one-way ANOVA. In primary neuron cultures, quantification of agonist-induced internalization was performed using real time confocal microscopy. The number of DOR-eGFP vesicles at various time points was counted from the corresponding videos. When internalization occurred it was completed by 60 min, and the number of DOR-eGFP vesicles at this time point was defined as 100%. Endocytosis efficiencies (E1/2) were defined as the time needed to internalize 50% of DOR-eGFP. ND indicates that weak or no change in surface labeling was detected. Data are mean±SEM for 4–9 independent experiments.