Regulation of epithelial sodium channels by the cystic fibrosis transmembrane conductance regulator.
Cystic fibrosis airway epithelia exhibit enhanced Na+ reabsorption in parallel with diminished Cl- secretion. We tested the hypothesis that the cystic fibrosis transmembrane conductance regulator (CFTR) directly affects epithelial Na+ channel activity by co-incorporating into planar lipid bilayers immunopurified bovine tracheal CFTR and either heterologously expressed rat epithelial Na+ channel ( alpha,b eta,gamma-rENaC) or an immunopurified bovine renal Na+ channel protein complex. The single channel open probability (Po) of rENaC was decreased by 24% in the presence of CFTR. Protein kinase A (PKA) plus ATP activated CFTR, but did not have any effect on rENaC. CFTR also decreased the extent of elevation of the renal Na+ channel Po following PKA-mediated phosphorylation. Moreover, the presence of CFTR prohibited the inward rectification of the gating of this renal Na+ channel normally induced by PKA-mediated phosphorylation, thus down-regulating inward Na+ current. This interaction between CFTR and Na+ channels occurs independently of whether or not wild-type CFTR is conducting anions. However, the nonconductive CFTR mutant, G551D CFTR, cannot substitute for the wild-type molecule. Our results indicate that CFTR can directly down-regulate single Na+ channel activity, thus accounting, at least in part, for the observed differences in Na+ transport between normal and cystic fibrosis-affected airway epithelia.
Ismailov
I I
II
Department of Physiology and Biophysics, University of Alabama at Birmingham, 35294-0005, USA.
Awayda
M S
MS
Jovov
B
B
Berdiev
B K
BK
Fuller
C M
CM
Dedman
J R
JR
Kaetzel
M
M
Benos
D J
DJ
D000255:Adenosine Triphosphate / Q000378:metabolism; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000494:pharmacology / Q000502:physiology*; D004553:Electric Conductivity; D004848:Epithelium / Q000502:physiology; D005260:Female; D015870:Gene Expression; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007679:Kidney Medulla / Q000502:physiology*; D008051:Lipid Bilayers; D008564:Membrane Potentials / Q000187:drug effects; D009865:Oocytes / Q000502:physiology; D010766:Phosphorylation; D017354:Point Mutation; D011494:Protein Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D015222:Sodium Channels / Q000096:biosynthesis / Q000302:isolation & purification / Q000502:physiology*
D008051:Lipid Bilayers; D011994:Recombinant Proteins; D015222:Sodium Channels; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000584:Amiloride; D000255:Adenosine Triphosphate; D011494:Protein Kinases