Summary
An asynchronous transport of individual secretory proteins has been recently described in the pancreas This asynchrony was observed in both unstimulated and stimulated conditions. It has also been proposed that unstimulated and stimulated secretions correspond to distinct secretory processes. Indeed according to that hypothesis, under resting conditions, a small fraction of the newly synthesized secretory proteins are channeled into a paragranular (vesicle) pathway while the residual proteins are packaged in the zymogen granules. These zymogen granules eventually move to the cell surface where their content is extruded by exocytosis. Under stimulated conditions the latter process is accelerated. Since the same type of asynchrony is observed under resting and stimulated conditions in the pancreatic juice, one can wonder if the hypothesis of a paragranular pathway is compatible with the observed asynchrony. In this review, an explantion is presented to account for the facts that following pulse and chase labelling, two waves of labelled proteins are released under resting secretions and secondly that asynchrony is maintained in both resting and stimulated conditions.
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Jamieson JD, Palade GE. Intracellular transport of secretory proteins in the pancreatic exocrine cell. Metabolic studies. J Cell Biol 1968;39:589–602.
Palade GE. Intracellular aspects of the process of protein synthesis. Science 1975;189:347–358.
Rothman SS. Protein transport by the pancreas. Science 1975;190:747–753.
Mroz EA, Lechêne C. Pancreatic zymogen granules differe markedly in protein composition. Science 1986;232:871–873.
Adelson JW, Miller PE. Pancreatic secretion by nonparallel exocytosis. Potential resolution of a long controversy. Science 1985;228:993–996.
Tartakoff AM, Jameison JD, Scheele GA, Palade GE. Studies on the pancreas of the guinea pig. Parallel processing and discharge of exocrine proteins. J Biol Chem 1975;256:2671–2677.
Scheele G, Tartakoff AM. Exit of non-glycosylated secretory proteins from the rough endoplasmic reticulum is asynchronous in the exocrine pancreas. J Biol Chem 1985;260:926–931.
Keller P, Cohen E, Neurath H. Enzymic composition of some cell fractions of bovine pancreas. J Biol Chem 1961;236:1407–1413.
Iovanna JD, Giorgi D, Dagorn JC. Newly synthesized amylase, lipase and serine proteases are transproted at different rates in rat pancreas. Digestion 1986;34:178–184.
Keim V, Rohr G. Evidence in vivo of asynchronous intracellular transport of rat pancreatic secretory proteins. Int J Pancreatol 1987;2:117–126.
Beaudoin AR, Grondin G. Pathways of secreation in the exocrine pancreas: The status of resting secretion. Life Sci 1987;40:2453–2460.
Roberge M, Beaudoin AR. Newly synthesized secretory proteins from pig pancreas are not released from a homogenous granule compartment. Biochim Biophys Acta 1982;716:331–336.
Beaudoin AR, Mercier M. Exocytosis in mammalian cells: VI. Temperature dependence of pancreatic exocrine secretion. Can J Physiol Pharmacol 1980;58:1509–1512.
Martinez-Alvino M, Beaudoin AR. The effect of metabolic inhibitors on pancreatic exocrine secretion from rabbit pancreas in vitro. IRCS Med Sci 1980;8:902–903.
Beaudoin AR, St-Jean P, Vachereau A. Asynchronism between amylase secretion and packaging in the zymogen granules of pig pancreas. Pancreas 1986;1:2–4.
Beaudoin AR, Vachereau A, St-Jean P. Evidence that amylase is release from two distinct pools of secretory proteins in the pancreas. Biochim Biophys Acta 1983;757:302–305.
Kramer MF, Poort C. Unstimulated secretion of protein from rat exocrine pancreas cells. J Cell Biol 1972;52:147–158.
Chang A, Arvan P. The exocrine pancreas from embryonic rats displays only constitutive secretion. J Cell Biol 1986;103:457a.
Arvan, P, Castle JD. Phasic release of newly synthesized secretory proteins in the unstimulated rat exocrine pancreas. J Cell Biol 1987;104:243–252.
Havinga J, Strous G, Poort C. Intracellular transport of the major glycoprotein of the zymogen granules in the rat pancreas. Eur J Biochem 1984;144:177–182.
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Beaudoin, A.R. The asynchronous transport of secretory proteins in the exocrine pancreas. Compatibility with the hypothesis of a paragranular pathway?. Int J Pancreatol 3, 409–414 (1988). https://doi.org/10.1007/BF02788199
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DOI: https://doi.org/10.1007/BF02788199