New observations on the ultrastructure of mammalian conducting airway epithelium: application of liquid propane freezing, deep etching, and rotary shadowing techniques to freeze-fracture.

Freshly isolated, viable hamster tracheal epithelium was rapidly frozen in a jet of liquid nitrogen-cooled propane followed by freeze-fracture, deep etching, and rotary shadowing. Examination of the replicas by transmission electron microscopy revealed characteristic features of both ciliated and nonciliated cells, profiles of tight junctional complexes, and two distinct types of membrane particle complexes. The findings of this study suggest that rapid freezing of viable biological specimens coupled with freeze-fracture, deep etching, and rotary shadowing may provide a useful approach to achieving some additional perspectives of cell structure and function. Since the experimental protocol avoided any use of chemical fixation and processing procedures generally employed in electron microscopy, this study also validates for airway epithelium the details of fine structure observed using more conventional ultrastructural methods.