Effect of tobacco smoke on MCC parameters in vitro. (a) Graph showing the experimental design. Abbreviations are: ASL (airway surface liquid), UC (Ussing chamber). (b) Upper left: representative traces of 10 µM CFTRinh172-induced short circuit current (Isc) changes after 10 µM forskolin stimulation of HBECs exposed to 10 µM amiloride. Tobacco smoke exposure of fully differentiated HBECs via the VC-10 smoking robot using 24 puffs of a total of 4 cigarettes (Kentucky 3R4F) reduced CFTR conductance 1 h after cigarette smoke exposure. Middle and upper right: Representation of CFTR channel activities of cells from smokers and non-smokers exposed to the air (middle) and smoke (right). Lower left: time course of CFTR activity after smoke or air exposure. Lower right: Decreased CFTR activity is represented by the different channel activities of smoked cells and cells exposed to air (ΔCFTR activity): ΔSmoke = CFTR activity of smoke-exposed cells – control cells exposed to air. (c) Upper left: Representative traces of ATP-induced (10 µM) short circuit current (Isc) changes in basolaterally permeabilized HBECs cells exposed to a basolateral-to apical K+ gradient in the presence of 10 µM amiloride. Middle and upper right: Representation of BK channel activities of cells from smokers and non-smokers exposed to air (middle) and smoke (right). Lower left: Cigarette smoke exposure decreased BK activity within 1 h of exposure (ATP elicited Isc after basolateral permeabilization and a basolateral to apical K+ gradient). Lower right: BK activity decrease is represented by the channel activity difference of smoke-exposed cells compared to air-exposed cells (ΔBK activity): ΔSmoke = BK activity of smoke-exposed cells – cells exposed to the air. (d) Smoke reduces ASL volume 2 h after exposure (meniscus scanning method) but (e) no change in transepithelial resistance (TER) is seen. All n ≥ 4 from ≥ 3 different lung donors. * indicates p < 0.05 compared to air exposure at the same time point.