Stickier mucus in CF?

• They have a non-functioning CFTR channel protein.

  Chloride ions go in, by active transport, but can't come out of epithelial cell into mucus by facilitated diffusion.

  Sodium ion channel protein is open, so sodium moves across apical membrane from mucus into epithelial cell, by facilitated diffusion.

  This increases solute conc in epithelial cell.

  So water moves from mucus into epitheliall cell, across apical membrane, by osmosis.

  This lowers water content of mucus, stickier mucus.