title: Ca2+ activates cystic fibrosis transmembrane conductance regulator- and Cl- -dependent HCO3 transport in pancreatic duct cells.
abstract: Pancreatic duct cells secrete bicarbonate-rich fluids, which are important for maintaining the patency of pancreatic ductal trees as well as intestinal digestive function. The bulk of bicarbonate secretion in the luminal membrane of duct cells is mediated by a Cl(-)-dependent mechanism (Cl(-)/HCO(3)(-) exchange), and we previously reported that the mechanism is CFTR-dependent and cAMP-activated (Lee, M. G., Choi, J. Y., Luo, X., Strickland, E., Thomas, P. J., and Muallem, S. (1999) J. Biol. Chem. 274, 14670-14677). In the present study, we provide comprehensive evidence that calcium signaling also activates the same CFTR- and Cl(-)-dependent HCO(3)(-) transport. ATP and trypsin evoked intracellular calcium signaling in pancreatic duct-derived cells through the activation of purinergic and protease-activated receptors, respectively. Cl(-)/HCO(3)(-) exchange activity was measured by recording pH(i) in response to [Cl(-)](o) changes of the perfusate. In perfusate containing high concentrations of K(+), which blocks Cl(-) movement through electrogenic or K(+)-coupled pathways, ATP and trypsin highly stimulated luminal Cl(-)/HCO(3)(-) exchange activity in CAPAN-1 cells expressing wild-type CFTR, but not in CFPAC-1 cells that have defective (DeltaF508) CFTR. Notably, adenoviral transfection of wild-type CFTR in CFPAC-1 cells completely restored the stimulatory effect of ATP on luminal Cl(-)/HCO(3)(-) exchange. In addition, the chelation of intracellular calcium by 1,2-bis(2-aminophenoxy)ethane-N,N,N,N'-tetraacetic acid (BAPTA) treatment abolished the effect of calcium agonists on luminal Cl(-)/HCO(3)(-) exchange. These results provide a molecular basis for calcium-induced bicarbonate secretion in pancreatic duct cells and highlight the importance of CFTR in epithelial bicarbonate secretion induced by various stimuli.
authors.affiliation: Department of Pharmacology and Brain Korea 21 Project for Medical Sciences and Department of Physiology, Yonsei University College of Medicine, Seoul 120-752, Korea.
authors.forename: Wan
authors.initials: W
authors.lastname: Namkung
authors.forename: Jin Ah
authors.initials: JA
authors.lastname: Lee
authors.forename: Wooin
authors.initials: W
authors.lastname: Ahn
authors.forename: WonSun
authors.initials: W
authors.lastname: Han
authors.forename: Sung Won
authors.initials: SW
authors.lastname: Kwon
authors.forename: Duk Sun
authors.initials: DS
authors.lastname: Ahn
authors.forename: Kyung Hwan
authors.initials: KH
authors.lastname: Kim
authors.forename: Min Goo
authors.initials: MG
authors.lastname: Lee
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000256:Adenoviridae / Q000235:genetics / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002460:Cell Line; D027963:Chloride-Bicarbonate Antiporters / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000378:metabolism; D016257:Fura-2 / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D010183:Pancreatic Ducts / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D044463:Receptor, PAR-1; D011983:Receptors, Purinergic / Q000378:metabolism; D018179:Receptors, Thrombin / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
chemical_list: D001639:Bicarbonates; C505032:CFTR protein, human; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D005456:Fluorescent Dyes; D044463:Receptor, PAR-1; D011983:Receptors, Purinergic; D018179:Receptors, Thrombin; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000255:Adenosine Triphosphate; D014357:Trypsin; D011188:Potassium; D002118:Calcium; D016257:Fura-2