Bile Acids Selectively Activate Iberiotoxin-sensitive Potassium Channels In Native Pancreatic Duct Cells

Abstract

Bile reflux into the pancreas is a common causes of acute pancreatitis. Our group has shown that luminal chenodeoxycholate (CDC) at low doses (0.1mM) stimulated HCO3- secretion in intact pancreatic ducts (Venglovecz et al. Gut. 2008). This stimulatory effect of CDC on HCO3- secretion was caused by an IP3-mediated elevation of intracellular calcium concentration and an increase in apical Cl-/HCO3- exchange activity. The aim of this work was to investigate whether CDC could also regulate ion channels in native pancreatic cells. Using standard whole cell current recordings (KCl-rich pipette: NaCl-rich bath solutions) exposure of isolated pancreatic duct cells to CDC (0.1 mM) reversibly increased whole cell currents ∼ 3-fold in 75 % of recordings (15/20 cells), and hyperpolarised membrane potential by ∼ 18 mV. Resting and activated currents showed marked outward rectification, and were moderately voltage-dependent. CDC-induced currents were inhibited by external barium (5 mM, n=6), as well as by the selective high conductance K+ channel blocker, iberiotoxin (100nM, n=7). However, they were not sensitive to TRAM34 (selective blocker of intermediate conductance K+ channels) nor UCL 1684 (selective blocker of small conductance K+ channels). Bile acid induced-activation was abolished when cytosolic Ca2+ buffering was increased with 5.0mM EGTA, and was only moderately reduced by removal of bath Ca2+. Higher concentrations of CDC (>0.5 mM) were deleterious if exposed for prolonged periods. Together these results provide strong evidence that low doses of CDC selectively activate iberiotoxin-sensitive K+ channels through an increase in cytosolic Ca2+, primarily from internal stores. Activation of a K+ conductance would hyperpolarise membrane potential and thereby increase the electrochemical driving force for HCO3- secretion through electrogenic apical anion exchangers. Supported by The Royal Society.