Characterization of cytosolic ca2+ signaling in rat bile duct
epithelia.
Nathanson, Michael H., Angela D. Burgstahler, Albert Mennone, and
James L. Boyer.
Liver Study Unit, Yale University School of Medicine, New Haven, CT
06520
APStracts 3:0037G, 1996.
Bile duct epithelia play an important role in the formation and
conditioning of bile. However, hormonal responses in this epithelial
tissue are incompletely understood. Secretin increases ductular
secretion through the intracellular messenger cAMP, but whether
hormones increase cytosolic Ca2+ (Cai2+) in these cells and whether
Cai2+ regu lates duct secretion is unknown. To address these
questions, we examined Cai2+ signaling in isolated rat bile duct
units using ratio microspectrofluorometry and confocal micros copy.
We also used video microscopy to examine secretion and cell volume in
isolated bile duct cells and duct units. Acetylcholine (ACh) and ATP
both increased Cai2+ in bile duct units and elicited patterns of
Cai2+ increases and oscillations that were distinct and dose
-dependent. In contrast, Cai2+ was not increased by the hepatocyte
Cai2+ agonists vasopressin, angiotensin and phenylephrine, or by the
exocrine pancreas agonists cholecys tokinin and bombesin. In
addition, secretin did not increase Cai2+ in the isolated bile duct
units, while ACh did not increase Cai2+ in isolated hepatocytes.
Mobilization of internal, thapsigargin-sensitive Ca2+ stores
contributed more than influx of extracellular Ca2+ to the Cai2+
increases induced in the duct units, and ATP-induced increases in
Cai2+ could be blocked by microinjection of heparin but not de-N
-sulfated heparin. ACh transiently decreased bile flow in the isolated
perfused rat liver, although neither ACh nor ATP al tered secretion
in isolated ducts or changed the volume of single isolated bile duct
cells. These findings demonstrate that bile duct epithelial cells
possess both muscarinic and purinergic receptors that activate Cai2+
signaling pathways which are similar to those seen in other types of
epithelia, but that the two types of receptors elicit distinct
patterns of Cai2+ signals. Increases in Cai2+ have minimal direct
effects on bile duct secretion, al though it remains to be determined
whether such signals selectively modulate other aspects of bile duct
epithelial cell function.
Received 29 September 1995; accepted in final form 31 January
1996.
APS Manuscript Number G422-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 14 February 96