Figure 1.

MOR-1 is expressed on the surface of TF-1 cells. (A) Western immunoblot analyses performed with the human neuroblastoma cell line SH-SY5Y (positive control) and TF-1 cell line whole cell lysates demonstrate the presence of μ-opioid receptor-1 protein (MOR-1) at ~50 KDa. Abrogation of the 50-KDa band with preincubation of the polyclonal antibody with a MOR-1 blocking peptide confirms the specificity of reaction. The membrane was stripped and reblotted for human β-actin (43 KDa) as the endogenous loading control. The blot is representative of results obtained from three independent experiments. (B) Flow cytometry of nonpermeabilized TF-1 cells stained with an antibody directed against a region mapping within the N-terminus of MOR-1 (20 μg/ml) shows expression on the cell surface. A fluorescein isothiocyanate (FITC)-conjugated secondary antibody directed against the primary host was used in combination with primary staining (blue) or alone (red) as a negative control. (C) The left panel shows a subpopulation of paraformaldehyde-fixed, nonpermeabilized TF-1 cells expressing MOR-1 on the surface (detected in green with a FITC-tagged antibody directed against a region mapping within the N-terminus of MOR-1). The right panel shows a merge with DAPI (4',6-diamidino-2-phenylindole) nuclear staining of the same field. The images were taken at 60× with an Olympus IX81 deconvolution microscope.