AJP - Gastrointestinal and Liver Physiology, Vol 267, Issue 1 40-G51, Copyright © 1994 by American Physiological Society
Nonparallel secretion of GP-2 from exocrine pancreas implies luminal coupling between acinar and duct cells
S. D. Freedman, K. Sakamoto and G. A. Scheele
Division of Gastroenterology, Charles A. Dana Research Institute, Boston, Massachusetts.
The in vivo and in vitro secretion of glycoprotein-2 (GP-2), a glycosyl
phosphatidylinositol (GPI)-anchored protein from the rat exocrine pancreas,
was characterized. GP-2 was secreted in a nonparallel manner compared with
amylase, a marker of secretory enzymes. Attenuated GP-2 secretion
correlated with hormones that stimulated exocytosis in acinar cells.
Augmented GP-2 secretion correlated with hormones that stimulated fluid and
bicarbonate secretion from ductal elements. Immunofluorescence studies
identified an enriched pool of GP-2 tightly bound to the apical membranes
of acinar cells in addition to zymogen granules. This non-zymogen granule
pool appears to represent the source of GP-2 released from acinar cells in
a nonparallel manner. With the use of dispersed pancreatic acini largely
devoid of ductal elements, GP-2 release was found to be augmented by
alkaline pH. Thus GP-2 secretion appears to be modulated by two discrete
cellular processes: 1) delivery of prereleased GP-2 within zymogen granules
to the ductal lumen by exocytic mechanisms and 2) enzymatic release of
GPI-anchored GP-2 from the luminal membranes, a kinetic process that
appears to be regulated by secretin- or carbachol-induced secretion of
bicarbonate.
