Comparison of the cytoskeleton in aortic endothelial cells in situ and in vitro.

Using fluorescence microscopy and a previously developed technique for making en face preparations of aortic endothelial cells (EC), we have compared the distribution of microtubules, centriolar regions, and microfilaments in porcine EC in situ with that in EC from the same source grown in monolayers in vitro. The results show that the cytoskeleton of EC undergoes considerable reorganization when EC are removed from the blood vessel and cultured. In vivo the microtubules run helically along the longitudinal axis of EC. It is not clear that all of these microtubules originate from the centriolar region which is located at one end of the nucleus, usually toward the heart. Prominent bundles of microfilaments extend almost the full length of the cell in a direction parallel to blood flow. In contrast, in EC in culture almost all of the microtubules radiate from a single prominent perinuclear microtubule-organizing center toward the cell periphery. In adjacent cells this microtubule-organizing center, which contains the centrioles, is randomly oriented with respect to the nucleus. The microfilaments in EC in vitro form a much more complex pattern in which circumferentially, radially, and longitudinally oriented bundles are evident. These results indicate that a dramatic rearrangement in these components of the cytoskeleton takes place when EC from the aorta are cultured in vitro and that care should be exercised in applying results of in vitro observations on EC to the cells of the endothelium lining blood vessels.