Ion composition and rheology of airway liquid from cystic fibrosis fetal tracheal xenografts

The composition of airway surface liquid (ASL) is partly determined by active ion and water transport through the respiratory epithelium. It is usually stated that in cystic fibrosis (CF), CF transmembrane conductance regulator protein abnormality results in imbalanced ion composition and dehydration of ASL, leading to abnormal rheologic and transport properties. To explore the relationship between ion composition, water content, and viscosity of airway liquid (AL), we used a human xenograft model of fetal airways developed in severe combined immunodeficiency (SCID) mice. Six non-CF and six CF portions of fetal tracheas were engrafted subcutaneously in the flanks of SCID mice raised in pathogen-free conditions. AL accumulated in the closed cylindric grafts was harvested 9 to 17 wk after implantation. At the time of AL sampling, all tracheal grafts displayed well-differentiated pseudostratified surface epithelium and submucosal glands. The viscosity of AL was measured using a controlled-stress rheometer. The ion composition of AL was quantified by X-ray microanalysis. No significant difference was observed for AL viscosity between non-CF (0.6 ± 0.5 Pa · s) and CF (0.2 ± 0.1 Pa · s) samples. In AL from non-CF and CF samples, the ion concentrations were Na: 63.9 ± 7.6, 79.7 ± 11.6; Cl: 64.9 ± 13.2, 82.6 ± 15.7; Mg: 1.9 ± 0.3, 2.2 ± 0.4; S: 4.9 ± 1.3, 4.8 ± 0.5; K: 2.4 ± 0.5, 3.2 ± 1.6; and Ca: 1.2 ± 0.3, 2.6 ± 0.8 mmol/liter, respectively. The ion composition of AL from CF versus non-CF xenografts was not significantly different. These results suggest that prior to inflammation and infection, the viscosity and ion composition of the fetal AL do not differ in CF and non-CF.