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

The pharmacological activation of the cystic fibrosis gene protein cystic f ibrosis transmembrane conductance regulator (CFTR) was studied in human air way epithelial Calu-3 cells, which express a high level of CFTR protein as assessed by Western blot and in vitro phosphorylation. Immunolocalization s hows that CFTR is located in the apical membrane. We performed iodide efflu x, 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 curr ent activated by X-33 or IBMX is linear, inhibited by glibenclamide and dip henylamine-2-carboxylate but not by DIDS or TS-TM calix[4] arene. Intracell ular 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 an d 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 m anipulating the chemical structure of xanthine derivatives offers an opport unity to identify further specific activators of CFTR in airway cells.