Decay of murine intestinal epithelial cells under extrusion.

Electron microscopic findings of this study revealed 2 types of extrusion of brush border cells from the summits of intestinal villi: a) By expansion of initial vacuolation the degenerating cell enlarges and elevates itself above the level of the extrusion zone. Cells about to lift become sphered and are shed into the lumen for degradation to continue. b) Another group of cells vacuolating to a similar extend already may start apical decay in situ. In this case mechanical elevation, apparently, is inefficient or retarded such as to offer a cell the opportunity to decompose at its proper place in the mucosal lining. Contrary to type A extrusion, i.e. the desquamation of the entire degenerating cell, type B produces cellular debris to be shed into the lumen. Either type of exfoliation may be associated with the formation of gaps the closure of which proceeds slowly. The light microscopic test of cell viability by means of horseradish peroxidase demonstrated many brush border cells leaky such as to become loaded with the tracer irrespective of its vascular or enteric approach to the extrusion zone. Damage of the cell membrane due to a brief pretreatment with digitonin resulted in a dramatic rise of horseradish peroxidase positive cells. With respect to these findings, one cannot escape the conclusion that both types of extrusion confer intermittent leakage on the summits of intestinal villi which at least could account for part of the diffusion of macromolecules in either direction.