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1 Division of Gastroenterology/Hepatology, Indiana University School of Medicine, Indianapolis, Indiana 46202; and 2 Department of Internal Medicine and Liver Center, Yale University School of Medicine, New Haven, Connecticut 06520
Bombesin, a neuropeptide, stimulates fluid
and HCO
3 secretion from
cholangiocytes, but the underlying mechanisms are poorly
understood. In this study, we aimed to examine the effects
of bombesin on ion transport processes involved in the regulation of
intracellular pH (pHi) and
HCO
3 secretion in polarized
cholangiocytes. Isolated bile duct units from normal rat liver were
used to measure pHi by
2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein 495 nm-to-440 nm dual ratio methods. Bombesin increased
Cl
-HCO
3 exchange
activity but did not affect basal pHi or the activities of
Na+/H+ exchange or
Na+-HCO
3 symport.
Depolarization of cholangiocytes increased basal
pHi and the activity of
Cl
/HCO
3
exchange, suggesting that an electrogenic Na+-HCO
3
symport might function as a counterregulatory pHi mechanism.
Na+-independent acid-extruding
mechanisms were not observed. We conclude that bombesin stimulates
biliary secretion from cholangiocytes by activating luminal
Cl
/HCO
3
exchange, which may be coupled to basolateral electrogenic
Na+-HCO
3 symport.
bicarbonate secretion; ion transport; chloride-bicarbonate exchange; electrogenic sodium-bicarbonate symport
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