Ultrastructural aspects of the transendothelial passage of macromolecules in the pulmonary trunk of the rat

: The authors examined the transendothelial passage of tracer macromolecules (feritin) in the endothelial cells of the lung stem of white rats (Wistar) by means of an electron microscope. They found that the feritin granules were detained by the pilous surface of the luminal cytolema at the initial phase of the process. This was enhanced also by luminal buds and invaginations respectively paraluminal canals, functioning as stagnating devices. The uptake and transcellular passage of the macromolecules was realized by micropinocytose vesicules, part of which were intracellularly and formed vacuole depots. Vesicules were formed from them secondarily, carrying the tracer mainly basaly. The authors observed also a bead roll pattern of transport vesicyles, which, passing tracer molecules one to another, formed functional trancellular canals for quick transport. There were certain dependences between the established forms of trancellular passage and the circulation time of feritin.