Ultrastructural characterization of epithelial cell membranes in normal human conducting airway epithelium: A freeze‐fracture study

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Abstract
Cell membranes of normal human nasal and tracheal epithelium were characterized by means of freeze‐fracture preparations. These investigations illustrated a predictable variability in the distribution of membrane‐associated particles on PF‐faces of different cell types and in different regions of the same cell. Details of the fine structure and variability of tight junctional complexes in different cell types are presented as are ultrastructural perspectives of cell membrane involvement in ciliogenesis and in mucus secretion. Because ciliogenic profiles and nascent tight junctional complexes were observed more frequently in nasal epithelial cells, these features provided markers of cellular differentiation. Based on the frequent appearance of such indicators, these observations suggested that cell turnover may be more rapid in the region of the nasal turbinates than in the trachea. There was no appreciable evidence of ultrastructural variability between the epithelial cell membranes of similar cell types in the upper and lower respiratory tract.