Airway epithelial cells--hyperabsorption in CF?

Airway epithelial cells transport electrolytes and are central to the disease cystic fibrosis (CF), which is an inherited transport defect affecting smaller airways and a number of other epithelial organs. Clinically, CF is dominated by a chronic lung disease, the main cause of morbidity and mortality. Airway obstruction by thick mucus and chronic infection by Pseudomonas aeruginosa eventually lead to loss of pulmonary function. Loss of function of CFTR Cl(-) channels was found to be the cause for CF. However, intensive research on the detailed mechanism of CF lung disease for more than 25 years produced a bewildering number of hypotheses and an endless discussion whether reduced Cl(-) secretion, primarily located in airway submucosal glands, or dehydration of the airways, driven by a hyperabsorption of Na(+) ions, is the primary cause of the disease. Recent results suggest a fine-tuned regulation of the airway fluid layer, but how significant really are Cl(-) and Na(+) transport?