Identification and regulation of the cystic fibrosis transmembrane conductance regulator-generated chloride channel

Cystic fibrosis transmembrane conductance regulator (CFTR) generates cAMP-regulated Cl channels; mutations in CFTR cause defective Cl^- channel function in cystic fibrosis epithelia. We used the patch-clamp technique to determine the single channel properties of Cl channels in cells expressing recombinant CFTR. In cell-attached patches, an increase in cellular cAMP reversibly activated low conductance Cl^- channels. cAMP-dependent regulation is due to phosphorylation, because the catalytic subunit of cAMP-dependent protein kinase plus ATP reversibly activated the channel in excised, cell-free patches of membrane. In symmetrical Cl^- solutions, the channel had a channel conductance of 10.4±0.2 (n = 7) pS and a linear current-voltage relation. The channel was more permeable to Cl^- than to I^- and showed no appreciable time-dependent voltage effects. These biophysical properties are consistent with macroscopic studies of Cl^- channels in single cells expressing CFTR and in the apical membrane of secretory epithelia. Identification of the single channel characteristics of CFTR-generated channels allows further studies of their regulation and the mechanism of ion permeation.