Dynamic regulation of CFTR bicarbonate permeability by [Cl-]i and its role in pancreatic bicarbonate secretion.
OBJECTIVE
Pancreatic bicarbonate (HCO3-) secretion is important for a healthy pancreas as well as digestive physiology. However, how human pancreatic duct cells secrete copious amounts of HCO3- has long been a puzzle. Here, we report that a dynamic increase in the cystic fibrosis transmembrane conductance regulator (CFTR) HCO3- permeability by intracellular Cl- concentration ([Cl-]i)-sensitive mechanisms plays a pivotal role in pancreatic HCO3- secretion.


METHODS
The role of [Cl-]i-sensitive kinases in CFTR-mediated HCO3- transport was examined in heterologous expression systems, PANC1 human pancreatic duct cells, and human and guinea pig pancreatic tissues using an integrated molecular and physiologic approach.


RESULTS
In human pancreatic tissues, CFTR-positive duct cells abundantly expressed with-no-lysine (WNK1) kinase, oxidative stress-responsive kinase 1 (OSR1), and sterile 20/SPS1-related proline/alanine-rich kinase (SPAK), which are known to be activated by low [Cl-]i. Interestingly, CFTR activation rapidly decreased [Cl-]i in response to luminal Cl- depletion in polarized PANC1 human pancreatic duct cells. Notably, the WNK1-mediated OSR1 and SPAK activation by low [Cl-]i strongly increased CFTR HCO3- permeability in CFTR-transfected HEK 293T, PANC1, and guinea pig pancreatic duct cells, making CFTR primarily an HCO3- channel, which is essential for the secretion of pancreatic juice containing HCO3- at a concentration greater than 140 mmol/L. In contrast, OSR1 and SPAK activation inhibited CFTR-dependent Cl-/HCO3- exchange activity that may reabsorb HCO3- from the high HCO3--containing pancreatic juice.


CONCLUSIONS
These results indicate that the [Cl-]i-sensitive activation of the WNK1-OSR1/SPAK pathway is the molecular switch to generate HCO3--rich fluid in the human pancreatic duct.
Park
Hyun Woo
HW
Department of Pharmacology, Institute of Gastroenterology, Brain Korea 21 Project for Medical Science, Seoul, Korea.
Nam
Joo Hyun
JH
Kim
Joo Young
JY
Namkung
Wan
W
Yoon
Jae Seok
JS
Lee
Jung-Soo
JS
Kim
Kyung Sik
KS
Venglovecz
Viktoria
V
Gray
Michael A
MA
Kim
Kyung Hwan
KH
Lee
Min Goo
MG
D000818:Animals; D017920:Antiporters / Q000235:genetics / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism*; D045744:Cell Line, Tumor; D002463:Cell Membrane Permeability; D016764:Cell Polarity; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D006168:Guinea Pigs; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008564:Membrane Potentials; D026901:Membrane Transport Proteins / Q000378:metabolism; D051379:Mice; D015778:Minor Histocompatibility Antigens; D010189:Pancreatic Juice / Q000378:metabolism; D020799:Pancrelipase / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000076988:Sulfate Transporters; D013997:Time Factors; D014162:Transfection; D000076204:WNK Lysine-Deficient Protein Kinase 1
D017920:Antiporters; D001639:Bicarbonates; C505032:CFTR protein, human; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D047908:Intracellular Signaling Peptides and Proteins; D026901:Membrane Transport Proteins; D015778:Minor Histocompatibility Antigens; C081011:SLC26A3 protein, human; C439529:SLC26A6 protein, human; D000076988:Sulfate Transporters; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D020799:Pancrelipase; C118135:OXSR1 protein, human; C116037:PAS domain kinases; D017346:Protein Serine-Threonine Kinases; D000076204:WNK Lysine-Deficient Protein Kinase 1; C498743:WNK1 protein, human