Newly Synthesized Amylase, Lipase and Serine Proteases Are Transported at Different Rates in Rat Pancreas

Abstract

The rates of intracellular transport of newly synthesized amylase, lipase, trypsinogen and chymotrypsinogen were compared in the anaesthesized rat pancreas by measuring their rates of secretion while keeping their relative rates of synthesis in a steady state. It is concluded that pancreatic proteins are not transported all at the same rate through the acinar cell. Among the four enzymes studied, proteolytic enzymes are transported faster than lipase, and amylase is the slowest. The relative rates of transport of these enzymes are not altered by secretory stimulation, since similar results were obtained in the basal state and under constant caerulein infusion (300 ng/kg/h).

The ER to Golgi Interface is the Major Concentration Site of Secretory Proteins in the Exocrine Pancreatic Cell

“…Thus we found no evidence for post‐translational increase of the immunoreactivity of Chtg, or the reverse for Am. Together with the results of the cycloheximide experiments in the previous section and the slow transport kinetics reported for Am (14–17), we take this as strong evidence that the relatively high labeling for Am indeed reflects its high concentration in the ER.…”

“…Since Am is the most abundant secretory protein of rat exocrine pancreatic cells, it was an obvious candidate to be probed in these previous studies. However, comparative biochemical analyses on several other pancreatic secretory proteins have indicated that Am stands alone in its slow secretion kinetics, probably because of enzymatic interactions of Am with ER membrane constituents (14–17). This notion is supported by our findings that Am is relatively enriched in ER cisternae (6,18).…”

Secretory pathways in animal cells: With emphasis on pancreatic acinar cells

“…It was thought, initially, that the different secretory proteins in pancreatic acinar cells were transported at the same rate from their site of synthesis through the various compartments of the intracellular route in unison (bulk flow type of transport) (Tartakoff et al, 1975). Recent studies, using more refined techniques, have shown an asynchrony in the release of different proteins secreted by the acinar cell under resting and stimulated conditions (Arvan and Castle, 1987;Iovanna et al, 1986;Keim and Rohr, 1987;Scheele and Tartakoff, 1985). Moreover, cell fractionation studies have indicated that this asynchrony is established at the level of the ER (Scheele and Tartakoff, 1985).…”

Pancreatic Juice Composition: New Views about the Cellular Mechanisms That Control the Concentration of Digestive and Nondigestive Proteins

“…According to this scheme, the newly synthesized proteins are sequestered in the rough endoplasmic reticu lum (RER), then transported to the transGolgi area. Recent data indicate an asyn chrony in the intracellular transport of secre tory proteins [24][25][26] which is already estab lished as the proteins exit from the RER [24], The asynchrony is maintained as the proteins move through or aside of the Golgi complex and reach the zymogen granule compartment. Since the same level of asyn chrony is maintained from the RER to the zymogen granule compartment, there must be a synchronized transport from the RER to the zymogen granule.…”

“…Since the same level of asyn chrony is maintained from the RER to the zymogen granule compartment, there must be a synchronized transport from the RER to the zymogen granule. Moreover, the asyn chrony is maintained as the proteins are released in resting and stimulated conditions [25,26], Since the early work of Greene et al [27], stimulated secretion has been widely be lieved to be an image of the overall zymogen granule composition. However, some recent observations support the view that there is a heterogeneity of zymogen granule composi tion in the same gland [28].…”