Microtubules are involved in transport of macromolecules by vesicles in cultured bovine aortic endothelial cells.

The macromolecular transport in bovine aortic endothelial monolayers, cultured in vitro, was studied by fluorescence microscopy, confocal laser scanning microscopy, and transmission electron microscopy. A fluid-phase endocytic tracer, fluorescein isothiocyanate dextran 70 kD (FITC-dextran 70), was found to be transported into and out of endothelial cells via vesicles arranged as chains stretching between the luminal surface and the cell interior and also from cell interior to the abluminal surface. The endocytic activity was reduced by colchicine, which disrupts microtubules, and increased during treatment with cytochalasin B, which blocks microfilament polymerization. These findings indicate that microtubules are required for fluid-phase endocytosis and that microfilaments hinder this process.