Phasic Release of Newly Synthesized Secretory Proteins in the Unstimulated Rat Exocrine Pancreas

• Published in: The Journal of cell biology Vol. 104; no. 2; pp. 243 - 252
• Main Authors: Arvan, Peter, Castle, J. David
• Format: Journal Article
• Language: English
• Published: New York, NY Rockefeller University Press 01.02.1987; The Rockefeller University Press
• Subjects: Acinar cells; Amylases - biosynthesis; Amylases - metabolism; Animals; Biological and medical sciences; Cell lines; Chymotrypsinogen - biosynthesis; Chymotrypsinogen - metabolism; Cytoplasmic Granules - metabolism; Endoplasmic Reticulum - metabolism; Enzyme Precursors - biosynthesis; Enzyme Precursors - isolation & purification; Enzyme Precursors - metabolism; Exocrine pancreas; Exocytosis; Fundamental and applied biological sciences. Psychology; Gels; Golgi apparatus; Golgi Apparatus - metabolism; Hepatocytes; In Vitro Techniques; Kinetics; Lipase - biosynthesis; Lipase - metabolism; Male; Molecular Weight; Pancreas; Pancreas - enzymology; Pancreas - metabolism; Pancreatic Hormones - biosynthesis; Pancreatic Hormones - isolation & purification; Pancreatic Hormones - metabolism; proteins; Rats; Rats, Inbred Strains; Secretion; Secretory vesicles; Trypsinogen - biosynthesis; Trypsinogen - metabolism; Vertebrates: digestive system; Zymogens; Vertebrata; Regulation(control); Mammalia; Rat; Digestive system; Secretion; Rodentia; Secretory protein; Biosynthesis; Biological rhythm; Pancreas
• DOI: 10.1083/jcb.104.2.243
• ISSN: 0021-9525

Pancreatic lobules from fasted rats secrete pulse-labeled proteins in two phases comprising 15 and 85% of basal output, respectively. The first (0-6.5 h) is initially (≤0.5 h) unstimulated by secretagogues, probably represents vesicular traffic of Golgi and post-Golgi origin (including condensing vacuoles/immature granules), and notably contains two groups of polypeptides with distinct release rates: (a) zymogens (t1/2∼ 2.4 h) and (b) minor nonzymogens plus one unique zymogen (t1/2∼ 1 h). The second phase (peak at 9-10 h) is stimulable, probably represents basal granule exocytosis (t1/2∼ 50 h), and contains zymogens exclusively. Newly synthesized proteins released in both phases appear asynchronously, reiterating their asynchronous transport through intracellular compartments. Zymogens in both phases are secreted apically. The sorting of first from second phase zymogen release does not appear to be carrier-mediated, although the sorting of zymogens from other secretory proteins may use this process. Finally, data are presented that suggest that both secretory phases are subject to physiologic regulation.