title: Calcium-dependent enzyme activation and vacuole formation in the apical granular region of pancreatic acinar cells.
abstract: The pancreatic acinar cell produces powerful digestive enzymes packaged in zymogen granules in the apical pole. Ca(2+) signals elicited by acetylcholine or cholecystokinin (CCK) initiate enzyme secretion by exocytosis through the apical membrane. Intracellular enzyme activation is normally kept to a minimum, but in the often-fatal human disease acute pancreatitis, autodigestion occurs. How the enzymes become inappropriately activated is unknown. We monitored the cytosolic Ca(2+) concentration ([Ca(2+)](i)), intracellular trypsin activation, and its localization in isolated living cells with specific fluorescent probes and studied intracellular vacuole formation by electron microscopy as well as quantitative image analysis (light microscopy). A physiological CCK level (10 pM) eliciting regular Ca(2+) spiking did not evoke intracellular trypsin activation or vacuole formation. However, stimulation with 10 nM CCK, evoking a sustained rise in [Ca(2+)](i), induced pronounced trypsin activation and extensive vacuole formation, both localized in the apical pole. Both processes were abolished by preventing abnormal [Ca(2+)](i) elevation, either by preincubation with the specific Ca(2+) chelator 1, 2-bis(O-aminophenoxy)ethane-N,N-N',N'-tetraacetic acid (BAPTA) or by removal of external Ca(2+). CCK hyperstimulation evokes intracellular trypsin activation and vacuole formation in the apical granular pole. Both of these processes are mediated by an abnormal sustained rise in [Ca(2+)](i).
authors.affiliation: Medical Research Council Secretory Control Research Group, Physiological Laboratory, and Departments of Surgery and Veterinary Preclinical Sciences, University of Liverpool, Liverpool L69 3BX, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Raraty
authors.forename: J
authors.initials: J
authors.lastname: Ward
authors.forename: G
authors.initials: G
authors.lastname: Erdemli
authors.forename: C
authors.initials: C
authors.lastname: Vaillant
authors.forename: J P
authors.initials: JP
authors.lastname: Neoptolemos
authors.forename: R
authors.initials: R
authors.lastname: Sutton
authors.forename: O H
authors.initials: OH
authors.lastname: Petersen
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002766:Cholecystokinin / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D007425:Intracellular Membranes / Q000502:physiology; D008564:Membrane Potentials; D051379:Mice; D008928:Mitochondria / Q000502:physiology; D010179:Pancreas / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D014357:Trypsin / Q000378:metabolism*; D014617:Vacuoles / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D002766:Cholecystokinin; D014357:Trypsin; D002118:Calcium