Fig. 5. Relative surface labeling of 5-HT_1BR and related mutants in transfected COS-7, LLC-PK1 cells and hippocampal neurons. Transfection of COS-7 cells (A) and hippocampal neurons (B) with Flag-5-HT_1B (wild type), Flag-LI379/380A-5-HT_1B or Flag-C384S-5-HT_1B. Surface staining with mouse monoclonal anti-Flag M2 antibody and intracellular labeling with rabbit anti-Flag after plasma membrane permeabilization are shown. Bars, 10 µm. (C) Quantification of the percentage of surface labeling of each construct in transfected COS-7 cells, LLC-PK1 cells and neurons. Data are expressed as mean relative surface labeling ± s.e.m. of 10-15 transfected cells per construct. **P<0.01, when compared with levels in the wild-type.