Regulation of pancreatic excretory function by ion channels 2015 Viktoria Venglovecz

Morphology of the pancreas

Composition of pancreatic juice 1–2 liters of pancreatic juice per day 1–2 liters of pancreatic juice per day acini secrete isotonic, plasma- like fluid acini secrete isotonic, plasma- like fluid pancreatic duct absorbs most of the Cl - and secrete HCO 3 + pancreatic duct absorbs most of the Cl - and secrete HCO 3 + Human, 140 mM HCO 3 + Human, 140 mM HCO 3 + Mouse and rat, 50–70mM HCO 3 + Mouse and rat, 50–70mM HCO 3 + The cation composition of the juice is nearly constant The cation composition of the juice is nearly constant

Fluid and electrolyte secretion by acinar cells

Na + /K + ATPase hydrolyzes ATP to exchange 3 Na + in for 2 K + out generate the transcellular Na + and K + gradients provides the electrochemical gradient determines the membrane potential.

K + channels Ca 2+ -activated K + channel Ca 2+ -activated K + channel BK channels BK channels IK channels IK channels

Na + /K + /2Cl - channels NKCC1 is ubiquitous NKCC1 is ubiquitous activated by cell shrinkage activated by cell shrinkage restore cell volume restore cell volume inhibited by the diuretics furosemide and bumetanide inhibited by the diuretics furosemide and bumetanide mediates 70% of the Cl - uptake mediates 70% of the Cl - uptake provide most of the Na + necessary to fuel the Na + /K + pump provide most of the Na + necessary to fuel the Na + /K + pump

Na + /H + and Cl - /HCO 3 + NHE1 and AE2 NHE1 and AE2 NHE1 and AE2 are ubiquitous NHE1 and AE2 are ubiquitous housekeepers of cytoplasmic pH housekeepers of cytoplasmic pH activated by small changes in intracellular pH activated by small changes in intracellular pH NHE1 is activated by acidic pHi NHE1 is activated by acidic pHi AE2 is activated by alkaline pHi AE2 is activated by alkaline pHi NHE1 and AE2 are involved in many cellular functions including mediation of acinar cell fluid and electrolyte NHE1 and AE2 are involved in many cellular functions including mediation of acinar cell fluid and electrolytesecretion

TMEM16A apical Ca 2+ -activated Cl - channel apical Ca 2+ -activated Cl - channel

AQUAPORINS AQP family consists of 13 members AQP family consists of 13 members water channels water channels glyceroporins glyceroporins AQPs functions: cell adhesion, proliferation, migration, and cell survival AQPs functions: cell adhesion, proliferation, migration, and cell survival Diseases: Sjögren’s syndrome and pancreatitis Diseases: Sjögren’s syndrome and pancreatitis Deletion of AQP5 disrupted the integrity of the tight junction and reduced the paracellular water permeability Deletion of AQP5 disrupted the integrity of the tight junction and reduced the paracellular water permeability

Fluid and electrolyte secretion by acinar cells Secretion is fueled by the basolateral Na + /K + ATPase pump Secretion is fueled by the basolateral Na + /K + ATPase pump NKCC1 and NHE1 are the main routes of Na + influx NKCC1 and NHE1 are the main routes of Na + influx Ca 2+ -activated K + channels set the membrane potential at 50 to 60 mV Ca 2+ -activated K + channels set the membrane potential at 50 to 60 mV NKCC1 is the major route of Cl - influx NKCC1 is the major route of Cl - influx NHE1 and AE2 set cytoplasmic pH at 7.2 NHE1 and AE2 set cytoplasmic pH at 7.2 Transcellular Na + flux Transcellular Na + flux

Fluid and electrolyte secretion by ductal cells

TRANSPORTERS AT THE BASOLATERAL MEMBRANE

Na + /H + exchanger 1 (NHE1) electroneutral 1Na + /1H + exchangers electroneutral 1Na + /1H + exchangers NHE1 NHE1 ubiquitous ubiquitous pHi homeostasis pHi homeostasis localized at the basolateral membrane localized at the basolateral membrane provide a portion of HCO 3 + influx provide a portion of HCO 3 + influx NHE2 and NHE3 NHE2 and NHE3 localized at the luminal membrane localized at the luminal membrane salvage HCO 3 + salvage HCO 3 +

TRANSPORTERS AT THE BASOLATERAL MEMBRANE

Na + /HCO 3 + exchanger (NBC) expressed at the BASOLATERAL membrane expressed at the BASOLATERAL membrane electroGENIC transporter electroGENIC transporter 1 Na + -2 HCO 3 + stoichiometry 1 Na + -2 HCO 3 + stoichiometry mediates the bulk of basolateral HCO 3 + entry mediates the bulk of basolateral HCO 3 + entry Acid-base homeostasis, Acid-base homeostasis, Regulation of cell volume and intracellular pH Regulation of cell volume and intracellular pH NBC1NBC3 expressed at the LUMINAL membrane expressed at the LUMINAL membrane electroNEUTRAL transporter electroNEUTRAL transporter 1 Na + -1 HCO 3 + stoichiometry 1 Na + -1 HCO 3 + stoichiometry Salvage HCO 3 + Salvage HCO 3 +

TRANSPORTERS AT THE BASOLATERAL MEMBRANE

TRANSPORTERS AT THE LUMINAL MEMBRANE

CFTR

MECHANISM OF HCO 3 + SECRETION

RELATIONSHIP BETWEEN ACINAR AND DUCTAL CELLS

fluid and HCO 3 - enzymes activating enzymes Physiology Pathophysiology STRESS AUTODIGESTION INFLAMMATION CELL DEATH DIGESTION Alcohol45% Bile45% Others 10%

Development of Acute Pancreatitis Inducing Factor - Bile acid - Ethanol -Other factors Intracinar Events -Pathological Ca 2+ signal -Colocalization of lysosomal enzymes and zymogens -Intrapancreatic trypsinogen activation -Autodigestion, Inflammation Immun Response -Leukocyte activation -Cytocines (IL-6, TNFα, etc.) -ROS ACUTE PANCREATITIS NO SPECIFIC THERAPY

The Pancreas

Ductal cells Acinar cells Insufficient electrolyte and fluid secretion by ductal cells in CF Destruction of acinar cells Primary defect in membrane trafficking of zymogens Correction of the luminal pH reverses the membrane trafficking defects and largely restores the membrane dynamics Pancreatic duct obstruction Freedman SD, Gastroenterology, 2001 Mislocalization of CFTR in AIP Decreased pancreatic ductal function Reversal by corticosteroid treatment Ko SB, Gastroenterology, 2010 c Model of post-ERCP pancreatitis in rats pH 6.9 pH 7.3 pH 6.0 Pancreatic damage Noble MD, Gut, 2008 Lower extracellular pH enhances secretagogue-induced zymogen activation Bhoomagoud M, Gastroenterology, 2009

Ductal cells Acinar cells alterations in pancreatic ductal fluid and bicarbonate secretion can increase patients’ risk to pancreatitis restoration of pancreatic ductal bicarbonate and fluid secretion may have therapeutic benefits

Alcohol Gallstone (bile acid) Trypsinogen → Trypsin ? ETIOLOGICAL FACTORS IN ACUTE PANCREATITIS

Venglovecz V et al. Gut 2008;57: Ignath I. et al. Pancreas 2009;38: Venglovecz V, et al. Gut 2011;60: Maleth J et al. Gut 2011;60:136-8.

Hegyi P. et al. Gut 2011;60: Maléth J. et al.unpiblished

The trypsin vicious cycle Pallagi et al, Gastroenterology 2011 Dec;141(6):

HCO 3 - To neutralize the acid content secreted by acinar cells HCO 3 - What are the roles of bicarbonate secretion? HCO 3 - To curtail trypsinogen autoactivation within the pancreatic ductal system To neutralise the acid chyme entering the duodenum from the stomach To defend the pancreas by washing out the toxic agents The main pancreatitis-inducing factors (bile acids and ethanol) are strong inhibitors of pancreatic ductal bicarbonate secretion