Guanylin regulates chloride secretion in the human gallbladder via the bile fluid.
OBJECTIVE
The biliary epithelium of bile ducts and gallbladder modifies the composition of primary hepatic bile by absorption and secretion of an electrolyte-rich fluid. The underlying transport mechanisms, however, are still incompletely understood. We investigated the expression, the cellular localization, and the functional role of guanylin, a bioactive intestinal peptide involved in the cystic fibrosis transmembrane conductance regulator (CFTR)-regulated electrolyte/water secretion, in the human gallbladder.


METHODS
Peptide-specific antibodies were raised to localize guanylin and its affiliated signaling proteins, i.e., the guanylin receptor, guanylate cyclase C (GC-C), cGMP-dependent protein kinase type II (cGKII), and CFTR in the human gallbladder and cholangiocarcinoma cells (Mz-Cha-1) by RT-PCR, Western blot, and immunocytochemistry. A sensitive ELISA was used to assess the range of guanylin concentration in human bile fluid. The functional role of guanylin was investigated in subconfluent Mz-Cha-1 cell monolayers by isotope efflux experiments.


RESULTS
Guanylin and its affiliated signaling proteins are highly expressed in the human gallbladder. Guanylin is localized to secretory epithelial cells of the gallbladder and is present in the bile, whereas GC-C, cGKII, and CFTR are confined exclusively to the apical membrane of the same epithelial cells. Functional studies in Mz-Cha-1 cells identify guanylin as a specific regulator of biliary Cl(-) secretion that very likely is mediated by an intracellular increase of cGMP-concentration.


CONCLUSIONS
Based on the present findings and on the functional role of guanylin in other epithelia, it is likely that gallbladder epithelial cells synthesize and release guanylin into the bile to regulate electrolyte secretion by a paracrine/luminocrine signaling pathway.
Department of Internal Medicine, Division of Gastroenterology, University Hospital Heidelberg, Germany. Hasan_Kulasiz@med.uni-heidelberg.de
Hasan
H
Kulaksiz
Thorsten
T
Schlenker
Daniel
D
Rost
Adolf
A
Stiehl
Martin
M
Volkmann
Thomas
T
Lehnert
Yalcin
Y
Cetin
Wolfgang
W
Stremmel
D001646:Bile / Q000502:physiology*; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D005704:Gallbladder / Q000378:metabolism*; D005768:Gastrointestinal Hormones / Q000502:physiology*; D006162:Guanylate Cyclase / Q000378:metabolism; D006801:Humans; D045265:Natriuretic Peptides; D010455:Peptides / Q000502:physiology*; D011506:Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014018:Tissue Distribution
C505032:CFTR protein, human; D002712:Chlorides; D005768:Gastrointestinal Hormones; D045265:Natriuretic Peptides; D010455:Peptides; D011506:Proteins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; C072685:guanylin; D000242:Cyclic AMP; D017869:Cyclic GMP-Dependent Protein Kinases; D006162:Guanylate Cyclase; D006152:Cyclic GMP