Heterogeneity of the composition and thickness of tracheal mucus in rats

Sims, David E., and Margaret M. Horne. Heterogeneity of the composition and thickness of tracheal mucus in rats. Am. J. Physiol. 273 (Lung Cell. Mol. Physiol. 17): L1036– L1041, 1997.—Inability to preserve airway mucus in situ has limited our understanding of its structure and function. This lightand transmission electron-microscopic study of rat tracheal mucus used a nonaqueous fixative that retains mucus (epiphase) over a lucent layer (hypophase). The fixative is a 1% solution of osmium tetroxide dissolved in a perfluorocarbon. The mean thickness of rat tracheal epiphase was 5 μm, with significant variation (0.1–50 μm) around the tracheal circumference. Tracheal mucus was thickest at the trachealis muscle region and contained cells, cellular debris, and a variable amount of surfactant and lipid, estimated at 4–16% of the total epiphase in five rats, with a mean composition of 9%. Lipid was observed on the surface of the epiphase, embedded within mucus, and at the epiphasehypophase interface. Refined study of developmental, physiological, and pathological alterations to the airway coat may benefit from this approach.