2 CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATOR MUTATIONS HAVE DIFFERENT EFFECTS ON BOTH PULMONARY PHENOTYPE AND REGULATION OF OUTWARDLY RECTIFIED CHLORIDE CURRENTS

Cystic fibrosis (CF), a disorder of electrolyte transport manifest in the lungs, pancreas, sweat duct, and vas deferens, is caused by mutati ons in the CF transmembrane conductance regulator (CFTR). The CFTR pro tein has been shown to function as a cAMP-activated chloride channel a nd also regulates a separate protein, the outwardly rectifying chlorid e channel (ORCC). To determine the consequence of disease-producing mu tations upon these functions, mutant CFTR was transiently expressed in Xenopus oocytes and in human airway epithelial cells lacking function al CFTR, Both G551D, a mutation that causes severe lung disease, and A 455E, a mutation associated with mild lung disease, altered but did no t abolish CFTR's function as a chloride channel in Xenopus oocytes. Ai rway epithelial cells transfected with CFTR bearing either A455E or G5 51D had levels of chloride conductance significantly greater than thos e of mock-transfected and lower than those of wild-type CFTR-transfect ed cells, as measured by chloride efflux. A combination of channel blo ckers and analysis of current-voltage relationships were used to disse ct the contribution of CFTR and the ORCC to whole cell currents of tra nsfected cells, While CFTR bearing either mutation could function as a chloride channel, only CFTR bearing A455E retained the function of re gulating the ORCC, These results indicate that CF mutations can affect CFTR functions differently and suggest that severity of pulmonary dis ease may be more closely associated with the regulatory rather than ch loride channel function of CFTR.