CHRNA4 and chronic obstructive pulmonary disease: Taken together, the studies in mouse and human airway epithelium regarding the regulation of mucociliary clearance by nAChR point towards nAChR, especially the α3β4 subtype, being a suitable therapeutic target for the stimulation of the mucociliary clearance under disease conditions in which it is impaired, such as in cystic fibrosis and in chronic obstructive pulmonary disease (COPD).