Ca2+-activated Cl- channels can substitute for CFTR in stimulation of pancreatic duct bicarbonate secretion.
This study addresses the mechanisms by which a defect in CFTR impairs pancreatic duct bicarbonate secretion in cystic fibrosis. We used control (PANC-1) and CFTR-deficient (CFPAC-1; DeltaF508 mutation) cell lines and measured HCO3- extrusion by the rate of recovery of intracellular pH after an alkaline load and recorded whole cell membrane currents using patch clamp techniques. 1) In PANC-1 cells, cAMP causes parallel activation of Cl- channels and of HCO3- extrusion by DIDS-sensitive and Na+-independent Cl-/HCO3- exchange, both effects being inhibited by Cl- channel blockers NPPB and glibenclamide. 2) In CFPAC-1 cells, cAMP fails to stimulate Cl-/HCO3- exchange and Cl- channels, except after promoting surface expression of DeltaF508-CFTR by glycerol treatment. Instead, raising intracellular Ca2+ concentration to 1 micromol/l or stimulating purinergic receptors with ATP (10 and 100 micromol/l) leads to parallel activation of Cl- channels and HCO3- extrusion. 3) K+ channel function is required for coupling cAMP- and Ca2+-dependent Cl- channel activation to effective stimulation of Cl-/HCO3- exchange in control and CF cells, respectively. It is concluded that stimulation of pancreatic duct bicarbonate secretion via Cl-/HCO3- exchange is directly correlated to activation of apical membrane Cl- channels. Reduced bicarbonate secretion in cystic fibrosis results from defective cAMP-activated Cl- channels. This defect is partially compensated for by an increased sensitivity of CF cells to purinergic stimulation and by alternative activation of Ca2+-dependent Cl- channels, mechanisms of interest with respect to possible treatment of cystic fibrosis and of related chronic pancreatic diseases.
Zsembery
A
A
*Department of General and Experimental Pathology, University of Vienna, Vienna, Austria.
Strazzabosco
M
M
Graf
J
J
D000255:Adenosine Triphosphate / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002586:Cesium / Q000494:pharmacology; D018118:Chloride Channels / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000502:physiology*; D005905:Glyburide / Q000494:pharmacology; D005990:Glycerol / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects; D009154:Mutation; D010183:Pancreatic Ducts / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology; D014407:Tumor Cells, Cultured
D001639:Bicarbonates; C505032:CFTR protein, human; D018118:Chloride Channels; D002712:Chlorides; D015221:Potassium Channels; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D002586:Cesium; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; C028019:cesium chloride; D005990:Glycerol; D005905:Glyburide; D002118:Calcium