TY - JOUR
T1 - Calcium-dependent regulation of secretion in biliary epithelial cells
T2 - The role of apamin-sensitive SK channels
AU - Feranchak, Andrew P.
AU - Doctor, R. Brian
AU - Troetsch, Marlyn
AU - Brookman, Kathryn
AU - Johnson, Sylene M.
AU - Fitz, J. Gregory
N1 - Funding Information:
Supported by the American Digestive Health Foundation Research Scholar Award; the American Gastroenterologic Association; the Children’s Digestive Health and Nutrition Foundation; the Cystic Fibrosis Foundation; the National Institute of Diabetes, Digestive, and Kidney Diseases (NIDDK) grant KO8 DK 61480 (to A.P.F.), DK 57729 and DK 34039 (to R.B.D.), and DK 43278 and DK 46082 (to J.G.F.).
PY - 2004/9
Y1 - 2004/9
N2 - Background & Aims: Increases in intracellular Ca2+ are thought to complement cAMP in stimulating Cl- secretion in cholangiocytes, although the site(s) of action and channels involved are unknown. We have identified a Ca2+-activated K+ channel (SK2) in biliary epithelium that is inhibited by apamin. The purpose of the present studies was to define the role of SK channels in Ca2+- dependent cholangiocyte secretion. Methods: Studies were performed in human Mz-Cha-1 cells and normal rat cholangiocytes (NRC). Currents were measured by whole-cell patch clamp technique and transepithelial secretion by Ussing chamber. Results: Ca2+-dependent stimuli, including purinergic receptor stimulation, ionomycin, and increases in cell volume, each activated K+-selective currents with a linear IV relation and time-dependent inactivation. Currents were Ca2+ dependent and were inhibited by apamin and by Ba2+. In intact liver, immunoflourescence with an antibody to SK2 showed a prominent signal in cholangiocyte plasma membrane. To evaluate the functional significance, NRC monolayers were mounted in a Ussing chamber, and the short-circuit current (Isc) was measured. Exposure to ionomycin caused an increase in Isc 2-fold greater than that induced by cAMP. Both the basal and ionomycin-induced Isc were inhibited by basolateral Ba2+, and ∼58% of the basolateral K + current was apamin sensitive. Conclusions: These studies demonstrate that cholangiocytes exhibit robust Ca2+-stimulated secretion significantly greater in magnitude than that stimulated by cAMP. SK2 plays an important role in mediating the increase in transepithelial secretion due to increases in intracellular Ca2+. SK2 channels, therefore, may represent a target for pharmacologic modulation of bile flow.
AB - Background & Aims: Increases in intracellular Ca2+ are thought to complement cAMP in stimulating Cl- secretion in cholangiocytes, although the site(s) of action and channels involved are unknown. We have identified a Ca2+-activated K+ channel (SK2) in biliary epithelium that is inhibited by apamin. The purpose of the present studies was to define the role of SK channels in Ca2+- dependent cholangiocyte secretion. Methods: Studies were performed in human Mz-Cha-1 cells and normal rat cholangiocytes (NRC). Currents were measured by whole-cell patch clamp technique and transepithelial secretion by Ussing chamber. Results: Ca2+-dependent stimuli, including purinergic receptor stimulation, ionomycin, and increases in cell volume, each activated K+-selective currents with a linear IV relation and time-dependent inactivation. Currents were Ca2+ dependent and were inhibited by apamin and by Ba2+. In intact liver, immunoflourescence with an antibody to SK2 showed a prominent signal in cholangiocyte plasma membrane. To evaluate the functional significance, NRC monolayers were mounted in a Ussing chamber, and the short-circuit current (Isc) was measured. Exposure to ionomycin caused an increase in Isc 2-fold greater than that induced by cAMP. Both the basal and ionomycin-induced Isc were inhibited by basolateral Ba2+, and ∼58% of the basolateral K + current was apamin sensitive. Conclusions: These studies demonstrate that cholangiocytes exhibit robust Ca2+-stimulated secretion significantly greater in magnitude than that stimulated by cAMP. SK2 plays an important role in mediating the increase in transepithelial secretion due to increases in intracellular Ca2+. SK2 channels, therefore, may represent a target for pharmacologic modulation of bile flow.
UR - http://www.scopus.com/inward/record.url?scp=4444361538&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=4444361538&partnerID=8YFLogxK
U2 - 10.1053/j.gastro.2004.06.047
DO - 10.1053/j.gastro.2004.06.047
M3 - Article
C2 - 15362045
AN - SCOPUS:4444361538
SN - 0016-5085
VL - 127
SP - 903
EP - 913
JO - Gastroenterology
JF - Gastroenterology
IS - 3
ER -