Size and dynamics of caveolae studied using nanoparticles in living endothelial cells.

Caveolae are plasma membrane invaginations prominent in all endothelial cells lining blood vessels. Caveolae characteristically bud to form free cytoplasmic vesicles capable of transporting carrier proteins such as albumin through the cell. However, caveolae size distribution and dynamics in living endothelial cells and ability of caveolae to internalize nanoparticles are not well understood. We demonstrate here the design of a dual-color nanoparticle pair to measure noninvasively caveolae size and dynamics. First, we coated nanoparticles with BSA (bovine serum albumin) to address whether albumin promoted their delivery. Albumin has been shown to bind to protein on endothelial cell surface localized in caveolae and activate albumin endocytosis. Imaging of BSA-coated nanoparticles varying from 20 to 100 nm in diameter in endothelial cells demonstrated that caveolae-mediated nanoparticle uptake was dependent on albumin coating of particles. We also showed that caveolae could accommodate up to 100 nm diameter nanoparticles, a size larger than the diameter of typical caveolae, suggesting compliant property of caveolae. Together, our results show the feasibility of tracking multicolored nanoparticles in living endothelial cells and potential usefulness for designing therapeutic nanoparticle cargo to cross the limiting vessel wall endothelial barrier.