Crater formation and endocytosis in human endothelial cells in vitro

The formation of craters under in vitro hypoxic conditions in the human venous endothelium was studied by scanning-(SEM) and transmission electron microscopy (TEM). Craters are a result of collapsed intracytoplasmatic vesicles which is probably due to extraction of fluid during processing. Thus craters are thought to be artefacts of preparation. This investigation indicates that fusion of caveolae is involved in intracytoplasmatic vesicle formation. A new quantitative method is described for studying endocytosis. Whole vein wall preparations immersed in isotonic saline (approximately 1 h) revealed reduced endocytotic activity in the luminal plasma membrane (LPM) of endothelial cells compared to the basal plasma membrane (BPM), where the endocytotic activity was increased.