Agonist-induced internalization and recycling of common and variant hOXTRs. (A) Fluorescent images of HEK-293 cells transfected with expression plasmids for the common-type hOXTR-376R and variants hOXTR-376G and hOXTR-R376C. Cells were double-labeled using antibody against the N-terminus of hOXTR (Alexa Fluor 488, green) and a nuclear marker (DAPI, blue). Images were obtained by confocal laser scanning microscopy at the indicated time points after the addition of OXT (100 nM). (B) Fluorescence intensities for hOXTRs were quantified and expressed as the percentage of receptors remaining at the cell surface. Data are mean ± standard error of the mean (n = 15 to 30 cells from five cultures). Statistical significance was evaluated by the Student’s t test (* P <0.05, **P <0.01; compared with hOXTR-376R).