CFTR and cystic fibrosis: In these studies it was found that, in contrast to the airways where CFTR is expressed together with the alternative calcium-activated chloride channel TMEM16A that remains intact in CF [32,33,34,35,36,37,38,39], CFTR is the dominant chloride channel responsible for chloride and fluid secretion in human colon [18,21,22,24,27,30].