FIGURE 3.

D₂ and D₃ receptors degrade. A–C, HEK293 cells expressing either D₂ (A), D₃ (B), or D₄ (C) were surface-biotinylated and incubated in the absence (NT) or presence of either dopamine (DA 10 μm, D₂ and D₄) or PMA (100 nm, D₃) for 30, 90, or 180 min. The fate of the surface-labeled receptors that had been protected after endocytosis was assessed after receptor immunoprecipitation followed by SDS-PAGE and streptavidin overlay. 100% lane shows total surface receptor labeled. Strip lane shows efficiency of thio cleavage. A representative immunoblot is shown. D–F, densitometric quantification (Scion Image) of D₂ (D), D₃ (E), and D₄ (F) receptor stability from experiments performed in A–C. Bars represent the mean recovery of surface-biotinylated receptors (relative to 30 min of stimulation). Data are represented as the mean of at least four independent experiments analyzed using one-way ANOVA with Bonferroni t test. ***, p ≤ 0.001; *, p ≤ 0.05 compared with 30 min of stimulation. ns, not significant.