Fig. 2. Receptor-mediated endocytic uptake of fluorescently-labeled lipoproteins by CHO cells. CHO cells were incubated with fluorescently-labeled lipoproteins in incubation medium for 15 minutes at 37°C, fixed with paraformaldehyde and mounted in mowiol (A-F). Single cells were imaged using fluorescence microscopy to visualize the accumulation of fluorescently-labeled ligands in endocytic vesicles. CHO(iLR) (A) and ldlA(iLR) (B) cells were incubated with Dil-LDL. HDLp labeled with DiI (C,D) or OG (E,F) was used to incubate CHO(iLR) (C,E) and wild-type CHO (D,F) cells. Uptake of fluorescently-labeled HDLp is reduced by an excess of unlabeled HDLp. CHO(iLR) cells were also incubated for 15 minutes at 37°C (G) or 30 minutes at 18°C (H,I) in incubation medium containing OG-HDLp in the absence (G,H) or presence (I) of a tenfold excess of unlabeled HDLp. Bars, 20 µm.