Novel regulation of cystic fibrosis transmembrane conductance regulator (CFTR) channel gating by external chloride.
The cystic fibrosis transmembrane conductance regulator (CFTR) is vital for Cl(-) and HCO(3)(-) transport in many epithelia. As the HCO(3)(-) concentration in epithelial secretions varies and can reach as high as 140 mm, the lumen-facing domains of CFTR are exposed to large reciprocal variations in Cl(-) and HCO(3)(-) levels. We have investigated whether changes in the extracellular anionic environment affects the activity of CFTR using the patch clamp technique. In fast whole cell current recordings, the replacement of 100 mm external Cl(-) ((Cl(o)(-))) with HCO(3)(-), Br(-), NO(3)(-), or aspartate(-) inhibited inward CFTR current (Cl(-) efflux) by approximately 50% in a reversible manner. Lowering Cl(o)(-) alone by iso-osmotic replacement with mannitol also reduced Cl(-) efflux to a similar extent. The maximal inhibition of CFTR current was approximately 70%. Raising cytosolic calcium shifted the Cl(-) dose-inhibition curve to the left but did not alter the maximal current inhibition observed. In contrast, a reduction in the internal [Cl(-)] neither inhibited CFTR nor altered the block caused by reduced Cl(o)(-). Single channel recordings from outside-out patches showed that lowering Cl(o)(-) markedly reduced channel open probability with little effect on unitary conductance. Together, these results indicate that alterations in Cl(o)(-) alone and not the Cl(-)/HCO(3)(-) ratio regulate the gating of CFTR. Physiologically, our data have implications for current models of epithelial HCO(3)(-) secretion and for the control of pH at epithelial cell surfaces.
Wright
Angela M
AM
Institute of Cell and Molecular Biosciences, University of Newcastle Upon Tyne, Framlington Place, Newcastle Upon Tyne, NE2 4HH, United Kingdom.
Gong
Xiandi
X
Verdon
Burns
B
Linsdell
Paul
P
Mehta
Anil
A
Riordan
John R
JR
Argent
Barry E
BE
Gray
Mike A
MA
D000818:Animals; D000838:Anions / Q000494:pharmacology; D002460:Cell Line; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000502:physiology*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects*; D009928:Organ Specificity; D010183:Pancreatic Ducts / Q000737:chemistry; D010539:Permeability; D017693:Sodium Bicarbonate / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology; D014162:Transfection
D000838:Anions; C505032:CFTR protein, human; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012965:Sodium Chloride; D017693:Sodium Bicarbonate