Properties of CFTR activated by the xanthine derivative X-33 in human airway Calu-3 cells

1 Laboratoire de Physiologie des Régulations Cellulaires, Unité Mixte de Recherche 6558, 86022 Poitiers; 2 Laboratoire de Chimie Organique, Faculté de Médecine et de Pharmacie, 86005 Poitiers, France; 3 Laboratorio di Genetica Molecolare, Istituto Giannina Gaslini, 16148 Genova, Italy; and 4 Department of Medical Biochemistry, University of Wales, College of Medicine, Cardiff CF14 4XN, United Kingdom The pharmacological activation of the cystic fibrosis gene protein cystic fibrosis transmembrane conductance regulator (CFTR) was studied in human airway epithelial Calu-3 cells, which express a high level of CFTR protein as assessed by Western blot and in vitro phosphorylation. Immunolocalization shows that CFTR is located in the apical membrane. We performed iodide efflux, whole cell patch-clamp, and short-circuit recordings to demonstrate that the novel synthesized xanthine derivative 3,7-dimethyl-1-isobutylxanthine (X-33) is an activator of the CFTR channel in Calu-3 cells. Whole cell current activated by X-33 or IBMX is linear, inhibited by glibenclamide and diphenylamine-2-carboxylate but not by DIDS or TS-TM calix[4]arene. Intracellular cAMP was not affected by X-33. An outwardly rectifying Cl current was recorded in the absence of cAMP and X-33 stimulation, inhibited by DIDS and TS-TM calix[4]arene. With the use of short-circuit recordings, X-33 and IBMX were able to stimulate a large concentration-dependent CFTR transport that was blocked by glibenclamide but not by DIDS. Our results show that manipulating the chemical structure of xanthine derivatives offers an opportunity to identify further specific activators of CFTR in airway cells. cystic fibrosis transmembrane conductance regulator; chloride conductance; pharmacology * L. Bulteau and R. Dérand contributed equally to these results.