Junctional adhesion mechanisms in airway basal cells.

The morphology of basal cells varies according to the height of the epithelium they are associated with. In taller epithelium, basal cells appear to have more tonofilaments (keratin filaments) than basal cells in shorter epithelium. We hypothesized that the changes in basal cell structure represent differentiation of junctional adhesion mechanisms related to the attachment strength necessary for the various-height epithelium. To evaluate this hypothesis, we used light- and electron-microscopic morphometry to quantitate junctional adhesion structures in basal cells from mice, rats, cats, rabbits, and sheep. The height of the tracheal columnar epithelium ranged from 12.0 microns in the mouse to 56.8 microns in the sheep. The volume density of basal cell keratin filaments ranged from 0.012 in the rat to 0.261 in the sheep and total desmosome length/basal cell profile (BCP) ranged from 0.08 microns to 1.77 microns, respectively. Total hemidesmosome length/BCP was similar in each airway sample. A close correlation was obtained between the height of the epithelium and the volume fraction of keratin filaments (r = 0.96) and total desmosome length/BCP (r = 0.94) in all airways studied. Total hemidesmosome length/BCP was not closely related to the height of the epithelium (r = 0.31). Based on these observations, we conclude that the basal cell is a differentiated cell with respect to junctional adhesion and a primary function of the airway basal cell is for attachment of columnar cells to the basal lamina.