 CFTR not only allows chloride ions to be drawn from the cell and into the ASL, but it also regulates another channel called ENac, which allows sodium ions to leave the ASL and enter the respiratory epithelium.CFTR normally inhibits this channel, but if the CFTR is defective, then sodium flows freely from the ASL and into the cell.As water follows sodium, the depth of ASL will be depleted and the cilia will be left in the mucous layer.