Fig. 4. Different colocalization of LAMP1 and endocytosed FGF1 after 2 hours. (A) HeLa cells were transiently transfected with FGFR1, 2, 3 or 4 and kept at 4°C with Cy3-FGF1 and 50 U/ml heparin for 2 hours. They were then washed and incubated in the presence of 0.3 mM leupeptin for 2 hours at 37°C. The cells were fixed, permeabilized and treated with mouse anti-LAMP1 primary antibody. The cells were further treated with Cy2-labelled anti-mouse secondary antibody and examined by confocal microscopy. Arrows point to colocalization in the case of FGFR1-3 and lack of colocalization in the case of FGFR4. Bar, 5 µm. (B) The percentage of FGF1-positive structures within cells that colocalized with LAMP1 was quantitated as described in Materials and Methods. Error bars denote the s.d.; n=15.