CFTR and cystic fibrosis: Early studies using Ussing chamber experiments on rectal tissues were pioneering in the field of CF research providing valuable insights into the pathophysiology of CFTR dysfunction (Mall et al., 1999; Veeze et al., 1991; Mall et al., 1998b; Veeze et al., 1994; Mall et al., 2000a; Mall et al., 2002; Mall et al., 2004a; Mall et al., 2000b; Roth et al., 2011).