ACTIVATION OF CHLORIDE CHANNELS IN NORMAL AND CYSTIC-FIBROSIS AIRWAY EPITHELIAL-CELLS BY MULTIFUNCTIONAL CALCIUM CALMODULIN-DEPENDENT PROTEIN-KINASE

CYSTIC fibrosis is associated with defective regulation of apical membrane chloride channels in airway epithelial cells. These channels in normal cells are activated by cyclic AMP-dependent protein kinase 1,2 and protein kinase C 3,4. In cystic fibrosis these kinases fail to activate otherwise normal Cl- channels 1-4. But Cl- flux in cystic fibrosis cells, as in normal cells, can be activated by raising intracellular Ca2+ (refs 5-10). We report here whole-cell patch clamp studies of normal and cystic fibrosis-derived airway epithelial cells showing that Cl- channel activation by Ca2+ is mediated by multifunctional Ca2+/calmodulin-dependent protein kinase. We find that intracellular application of activated kinase and ATP activates a Cl- current similar to that activated by a Ca2+ ionophore, that peptide inhibitors of either the kinase or calmodulin block Ca2+-dependent activation of Cl- channels, and that a peptide inhibitor of protein kinase C does not block Ca2+-dependent activation. Ca2+/calmodulin activation of Cl- channels presents a pathway with therapeutic potential for circumventing defective regulation of Cl- channels in cystic fibrosis.