Fusion of pinocytotic vesicles in liquid filled lungs: a mechanism of cellular damage.

Lungs of anesthetized rabbits were filled unilaterally with macromolecule-containing solutions (Dextran 40 and albumin) for 20 min. which generally resulted in fluid resorption from the flooded lung. Electron microscopic examination revealed the following: (1) formation of chains of vesicles, similar or identical to pinocytotic vesicles, which start from depressions or fluid-immersed cellular surfaces in macrophages, or endothelial and squamous epithelial cells; and (2) formation of intracellular blisters as a result of the apparent fusion of numerous pinocytotic vesicles. Both observations seem to be augmented forms of normal phenomena. The hypothesis is advanced that the chains of vesicles are related to the increased amount of undulation of the cell surface and to cellular invaginations that follow relaxation of tensions at the surface of cells immersed in fluid. The blisters could be the result of the increase of bidirectional flow of vesicles across the squamous cells. This brings an increased risk of collision because of the absence of lysosomes in the thin cytoplasmic extensions of endothelial and squamous epithelial cells. It is concluded that, even in very early stages, flooding per se produced some form of cellular alterations with a potential for leading to more overt lung pathology such as cell death and desquamation which would greatly increase tissue permeability.