Heparin treatment removes secreted FGF2-GFP from cell surfaces. Time-lapse video (10 s/frame) of FGF2-GFP expressing cells treated with heparin (1 mg/ml). CHO-K1 cells were induced for 24 h with doxycycline followed by labeling with Alexa Fluor 647–labeled anti-GFP nanobodies. Heparin was added after 5 min following the start of image acquisition. Left: Total GFP fluorescence is recorded. Right: The secreted population of FGF2-GFP was detected by anti-GFP nanobody labeling. Bar, 10 µm.
