AJP - Gastrointestinal and Liver Physiology, Vol 239, Issue 5 335-G347, Copyright © 1980 by American Physiological Society
Messenger role of calcium in function of pancreatic acinar cells
I. Schulz
Enzyme secretion from the exocrine pancreas is elicited by a) cholinergic
stimulants, b) hormones belonging to the family of pancreozymin, c) some
amphibian peptides such as bombesin, eledoisin, and physalaemin, and d)
secretin and vasoactive intestinal polypeptide. Whereas the mechanism of
the group d hormones in stimulating enzyme secretion involves adenosine
3',5'-cyclic monophosphate, the others seem to use a common pathway
involving Ca2+ as intracellular messenger and probably guanosine
3',5'-cyclic monophosphate as modulator of their action. Their effects can
be ascribed to two processes. One pathway involves release of Ca2+ from an
intracellular store that is most likely located in the plasma membrane.
This phase is independent of extracellular Ca2+ and leads to a rise of
guanosine 3',5'-cyclic monophosphate. The other pathway is characterized by
an increased permeability of the plasma membrane for Ca2+ and is necessary
for sustained secretion. Both pathways lead to an increase cytosolic-free
Ca2+ concentration. Ca2+ is either directly involved in fusion of zymogen
granules with the luminal cell membrane or triggers events that lead to
exocytosis. Furthermore, augmented cytosolic-free calcium concentration a)
increased the plasma membrane permeability for Na+, Cl-, and K+, which
leads to depolarization of the cell, and b) induces uncoupling of
neighboring acinar cells.
