Airway surface liquid composition in mice

Airway surface liquid (ASL) lines the conducting airways of the respiratory tract. We collected small samples of this liquid from the lower tracheae o f anesthetized C57BL/6 mice and determined its ionic composition (in mM: 87 .2 Na+, 4.7 K+, and 57.0 Cl-). Intravenous methacholine produced significan t increases in the concentrations of Na+, K+, and Cl- within ASL. A limited analysis of liquid from cystic fibrosis transmembrane conductance regulato r (CFTR) knockout mice revealed no significant differences compared with li ttermate controls; however, Pseudomonas aeruginosa infection led to an incr ease in the salt concentration of ASL in cftr(+/+) mice. Morphometric measu rements of tracheal submucosal gland volume revealed significant difference s between inbred mouse strains, corresponding to ease of ASL collection. We conclude that although submucosal glands may be responsible for the produc tion of some ASL, the ionic composition of this liquid is actively regulate d by the underlying epithelial cells.