CFTR and irritable bowel syndrome: CFTR: cystic fibrosis transmembrane conductance regulator; cGMP: cyclic guanosine monophosphate; CLC2: chloride channel; GC-C: guanylyl cyclase-C receptor; NHE3: sodium–hydrogen exchanger; CIC: chronic idiopathic constipation; IBS-C: constipation-predominant irritable bowel syndrome