Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR), which forms a chloride ion (Cl^-) transport channel in epithelial cells. But the existence of some CF patients with normal Cl^- ion channel activity has puzzled researchers for some time.

In 1 March Nature, Shmuel Muallem and colleagues from the University of Texas Southwestern Medical Center, Dallas report that disruption in the transport of bicarbonate ions (HCO₃^-) may also be of considerable importance in CF patients (Nature 2001, 410:94-97).

They measured HCO₃^- and Cl^- transport in cells transfected with DNA encoding wild-type or mutant CFTR. In 11 common mutations of CFTR, the transport of HCO₃^- was more greatly impaired than that of Cl^-.

It is lung disease that accounts for most of the mortality in...