Fig. 5.

Effects of cocaine on internalization of D₂R^YFP in HEK cells in the absence or presence of coexpression of Sigma1R. In the upper part, a cocaine concentration response curve on D₂R^YFP internalization is illustrated in red. To the right, quantitation of the D₂R^YFP internalization is found. With increasing concentrations, cocaine produces marked internalization of D₂R^YFP which is counteracted by expression of Sigma1R (D₂R (LogEC50 = −7.04 ± 0.09), D₂R-δ1R (LogEC50 = −6.63 ± 0.40)). In the lower part, the time-course of the action of cocaine is found in the D₂R cDNA-transfected cells in the absence or presence of Sigma1R cDNA cotransfection. Cocaine (100 nM) induces a marked internalization of D₂R^YFP construct in the first hour. This action is again counteracted by the coexpression of Sigma1R with a high significance. These results are illustrated in the left lower panels, and the quantitation is found in the right lower panel. The data represent the means ± S.E.M. of three independent experiments performed with a total of eight replicates each. Statistical analysis was performed by two-way ANOVA (***P < 0.001)