Activation of chloride channels in normal and cystic fibrosis airway epithelial cells by multifunctional calcium/calmodulin-dependent protein kinase

Abstract

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.