Nonparallel secretion of GP-2 from exocrine pancreas implies luminal coupling between acinar and duct cells.
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.
Freedman
S D
SD
Division of Gastroenterology, Charles A. Dana Research Institute, Boston, Massachusetts.
Sakamoto
K
K
Scheele
G A
GA
D000681:Amylases / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002450:Cell Communication; D005455:Fluorescent Antibody Technique; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D001639:Bicarbonates; D017261:Glycosylphosphatidylinositols; D008562:Membrane Glycoproteins; C072961:glycoprotein-2, pancreas; D000681:Amylases