Figure 5. Endocytosis of gold-labeled albumin occurs in cav-1^+/+ MLEC (a-d) through caveolae-dependent and -independent pathways but only through caveolae-independent pathway in cav-1^-/- MLEC (e-g).

Both caveolae vesicles (black arrow) and clathrin-coated pits (black arrowhead) were positive for gold-labeled albumin (a-c) suggestive of internalization via a non-caveolin-1 dependent endocytic mechanism in cav-1^+/+ MLEC. Although cav-1^-/- MLEC lack classical caveolae vesicles, there was detectable transport of gold labeled albumin to endosome and clathrin-coated pits were involved in the process (e-g). Cells were plated into a 6-well plate and grown until confluent. After serum starvation for 4 hr, cells were incubated with gold-labeled BSA in cold HBSS and moved to 4°C for 1 hr followed by warming at 37°C for up to 40 min. Cells were fixed and images were taken by transmission electron microscopy (80000× magnification).