FIGURE 1.

Endocytosis of the D₂, D₃, and D₄ receptors. A, HEK293 cells stably expressing N-terminally FLAG-tagged D₂, D₃, or D₄ were incubated with anti-FLAG antibody and then were either left untreated or treated with 10 μm dopamine, 10 μm quinpirole, or 100 nm PMA for 45 min. Cells were then fixed, permeabilized, and incubated with Alexa Fluor® 488-conjugated anti-mouse antibody. Shown are representative confocal images. B–D, endocytosis of the D₂-like receptors at 10, 20, 45, and 90 min was quantified using flow cytometry (see “Materials and Methods”). D₂ and D₄ receptors endocytosed in response to dopamine (B) and quinpirole (C), whereas D₃ receptors endocytosed only in response to PMA (D). Data are represented as the mean of at least four independent experiments performed in duplicate analyzed using one-way ANOVA with Bonferroni t test. ***, p ≤ 0.001, D₂, D₃, and D₄ compared with untreated controls.