FIGURE 9.

Effect of siRNA-mediated suppression of endogenous GRK2 expression on D₂ DAR surface expression and internalization. HEK293T cells were transfected with either control siRNA or GRK2 siRNA followed by transfection with the D₂ DAR. A, endogenous GRK2 expression level was assessed by Western blotting using an anti-GRK2 antibody as described under “Experimental Procedures.” Representative data from four independent experiments are shown. B, the cells were incubated in the absence (C) or presence of 10 μm DA for 1 h and then subjected to intact cell [³H]sulpiride binding assays as described under “Experimental Procedures.” C, the internalization of the D₂ DAR was assessed by measuring the decrease in cell surface [³H]sulpiride binding sites, and the data are expressed as the percent loss of cell surface receptors. The values shown represent the means ± S.E. of four independent experiments. *, p < 0.05, unpaired Student's t test.