CFTR-dependent Cl− secretion in Xenopus laevis lung epithelium

In our present study we used preparations from Xenopus laevis lungs to perform electrophysiological Ussing chamber measurements, unidirectional flux measurements, and employed molecular approaches to elucidate the presence and function of a cystic fibrosis transmembrane conductance regulator (CFTR) homolog in this tissue. Application of different CFTR blockers (NPPB (5-nitro-2-(3-phenylpropylamino)benzoic acid), niflumic acid (NFA), glibenclamide, lonidamine, CFTRinh-172) to the apical side of the tissues was able to significantly decrease the measured short circuit current (ISC) indicating a Cl− secretion due to luminal located CFTR channels. This was further supported by a net 36Cl− secretion determined by radioactive tracer flux experiments. Further, Xenopus pulmonary epithelia responded to apical chlorzoxazone exposure – a CFTR activator – and this activated current was inhibited by CFTRinh-172. We performed reverse transcription-PCR (RT-PCR) and Western blot analysis and with both approaches we found characteristic signals indicating the presence of a CFTR homolog in Xenopus lung. In addition, we were able to detect CFTR in apical membranes of Xenopus lung slices with immunohistological techniques. We conclude that Xenopus lung epithelium exhibits functional CFTR channels and that this tissue represents a valuable model for the investigation of ion transport properties in pulmonary epithelia.