TY - JOUR
T1 - Secretin promotes osmotic water transport in rat cholangiocytes by increasing aquaporin-1 water channels in plasma membrane. Evidence for a secretin-induced vesicular translocation of aquaporin-1
AU - Marinelli, Raul A.
AU - Pham, Linh
AU - Agre, Peter
AU - LaRusso, Nicholas F.
N1 - Copyright:
Copyright 2007 Elsevier B.V., All rights reserved.
PY - 1997/5/16
Y1 - 1997/5/16
N2 - Although secretin is known to stimulate ductal bile secretion by directly interacting with cholangiocytes, the precise cellular mechanisms accounting for this choleretic effect are unknown. We have previously shown that secretin stimulates exocytosis in cholangiocytes and that these cells transport water mainly via the water channel aquaporin-1 (AQP1). In this study, we tested the hypothesis that secretin promotes osmotic water movement in cholangiocytes by inducing the exocytic insertion of AQP1 into plasma membranes. Exposure of highly purified isolated rat cholangiocytes to secretin caused significant, dose-dependent increases in osmotic membrane water permeability (P(f)) (e.g. increased by 60% with 10-7 M secretin), which was reversibly inhibited by the water channel blocker HgCl2. Immunoblotting analysis of cholangiocyte membrane fractions showed that secretin caused up to a 3-fold increase in the amount of AQP1 in plasma membranes and a proportional decrease in the amount of the water channel in microsomes, suggesting a secretin-induced redistribution of AQP1 from intracellular to plasma membranes. Both the secretin-induced increase in cholangiocyte P(f) and AQP1 redistribution were blocked by two perturbations that inhibit secretin-stimulated exocytosis in cholangiocytes, i.e. treatment with colchicine and exposure at low temperatures (20 and 4 °C). Our results demonstrate that secretin increases AQP1-mediated P(f) in cholangiocytes. Moreover, our studies implicate the microtubule-dependent vesicular translocation of AQP1 water channels to the plasma membrane, a mechanism that appears to be essential for secretin-induced ductal bile secretion and suggests that AQP1 can be regulated by membrane trafficking.
AB - Although secretin is known to stimulate ductal bile secretion by directly interacting with cholangiocytes, the precise cellular mechanisms accounting for this choleretic effect are unknown. We have previously shown that secretin stimulates exocytosis in cholangiocytes and that these cells transport water mainly via the water channel aquaporin-1 (AQP1). In this study, we tested the hypothesis that secretin promotes osmotic water movement in cholangiocytes by inducing the exocytic insertion of AQP1 into plasma membranes. Exposure of highly purified isolated rat cholangiocytes to secretin caused significant, dose-dependent increases in osmotic membrane water permeability (P(f)) (e.g. increased by 60% with 10-7 M secretin), which was reversibly inhibited by the water channel blocker HgCl2. Immunoblotting analysis of cholangiocyte membrane fractions showed that secretin caused up to a 3-fold increase in the amount of AQP1 in plasma membranes and a proportional decrease in the amount of the water channel in microsomes, suggesting a secretin-induced redistribution of AQP1 from intracellular to plasma membranes. Both the secretin-induced increase in cholangiocyte P(f) and AQP1 redistribution were blocked by two perturbations that inhibit secretin-stimulated exocytosis in cholangiocytes, i.e. treatment with colchicine and exposure at low temperatures (20 and 4 °C). Our results demonstrate that secretin increases AQP1-mediated P(f) in cholangiocytes. Moreover, our studies implicate the microtubule-dependent vesicular translocation of AQP1 water channels to the plasma membrane, a mechanism that appears to be essential for secretin-induced ductal bile secretion and suggests that AQP1 can be regulated by membrane trafficking.
UR - http://www.scopus.com/inward/record.url?scp=0031011414&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0031011414&partnerID=8YFLogxK
U2 - 10.1074/jbc.272.20.12984
DO - 10.1074/jbc.272.20.12984
M3 - Article
C2 - 9148905
AN - SCOPUS:0031011414
SN - 0021-9258
VL - 272
SP - 12984
EP - 12988
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 20
ER -