Calcium-dependent enzyme activation and vacuole formation in the apical granular region of pancreatic acinar cells

Proc Natl Acad Sci U S A. 2000 Nov 21;97(24):13126-31. doi: 10.1073/pnas.97.24.13126.


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).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / physiology*
  • Calcium Signaling / physiology*
  • Cholecystokinin / pharmacology
  • Cytoplasmic Granules / drug effects
  • Cytoplasmic Granules / physiology
  • Cytoplasmic Granules / ultrastructure
  • Cytosol / metabolism
  • Enzyme Activation
  • Intracellular Membranes / physiology
  • Membrane Potentials
  • Mice
  • Mitochondria / physiology
  • Pancreas / cytology*
  • Pancreas / drug effects
  • Pancreas / physiology*
  • Trypsin / metabolism*
  • Vacuoles / drug effects
  • Vacuoles / physiology*
  • Vacuoles / ultrastructure


  • Cholecystokinin
  • Trypsin
  • Calcium