Visualization of channel-activating protease (CAP) activity by peptide-based FRET probes

Introduction: The epithelial sodium channel (ENaC) plays a crucial role in sodium transport across epithelial membranes and in the homeostasis of airway surface liquid (ASL) hydration. Proteolytic cleavage of the ENaC γ-subunit by channel-activating proteases (CAPs) increases the opening probability of the channel and thereby enhances sodium transport. Tarran and co-workers have shown that CAP expression is elevated in primary bronchial epithelial cultures of CF patients compared to tissue from healthy subjects (Tarran et al., 2006). However, the impact of CAPs on ENaC activity in cystic fibrosis lung disease is…