Abstract
The gene mutated in cystic fibrosis codes for the cystic fibrosis transmembrane conductance regulator (CFTR). Previously, we provided definitive evidence that CFTR functions as a phosphorylation-regulated chloride channel in our planar lipid bilayer studies of the purified, reconstituted protein. Recent patch-clamp studies have lead to the suggestion that CFTR may also be capable of conducting ATP or inducing this function in neighboring channels. In the present study, we assessed the ATP channel activity of purified CFTR and found that the purified protein does not function as an ATP channel in planar bilayer studies of single channel activity nor in ATP flux measurements in proteoliposomes. Hence, CFTR does not possess intrinsic ATP channel activity and its putative role in cellular ATP transport may be indirect.
Highlights
The function of CFTR1 as a phosphorylation and ATP-regulated chloride channel is thought to be critical for the elaboration of salt and water secretion across the epithelial cell lining of multiple organs; the airways, pancreatic ductules, gastrointestinal tract, and reproductive tract [1]
It has been suggested that CFTR may interact with another type of chloride channel found in the apical membrane of epithelial cells, the outwardly rectifying chloride channel (ORCC)
In order to directly assess the capacity of CFTR to conduct ATP, we first compared the single channel activity of purified CFTR reconstituted in planar lipid bilayers in the presence of symmetrical chloride (140 mM KCl) solutions with activity detected in the presence of symmetrical K2-ATP (140 mM) solutions
Summary
The function of CFTR1 (the cystic fibrosis transmembrane conductance regulator) as a phosphorylation and ATP-regulated chloride channel is thought to be critical for the elaboration of salt and water secretion across the epithelial cell lining of multiple organs; the airways, pancreatic ductules, gastrointestinal tract, and reproductive tract [1]. We sought to assess the intrinsic ATP channel activity of CFTR by examining the conductance properties of purified, reconstituted CFTR.
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