Disassembly of rat pancreatic acinar cell cytoskeleton during supramaximal secretagogue stimulation

Abstract

In vivo stimulation of the exocrine pancreas with concentrations of secretagogue in excess of a maximally stimulating dose causes a marked disturbance of the intracellular segregation, transport, and exocytosis of digestive enzyme zymogens. Under physiological conditions elements of the cytoskeleton, most notably microtubules and microfilaments, are involved in the regulation of these intracellular events. We infused caerulein, a peptide analogue of cholecystokinin, at a supramaximal dose (10 micrograms.kg-1.h-1 for up to 6 h) intravenously in rats. To study the ultrastructural alterations of acinar cell microfilaments and microtubules by immunogold labeling, we used monoclonal antibodies directed against actin and beta-tubulin. As early as 30 min after the start of the secretagogue infusion we found a progressive disassembly of microtubules and microfilaments in exocrine cells. In immunoblot studies this disassembly of the cytoskeleton was paralleled by a degradation of its structural proteins actin and beta-tubulin. Our results indicate that the earliest morphological events during supramaximal secretagogue stimulation of the pancreas involve the disassembly and degradation of microtubules and microfilaments. This cell biological phenomenon offers an explanation for the disturbances of segregation, transport, and exocytosis of digestive enzymes, which are known to be associated with supramaximal stimulation of the pancreas and experimental models of pancreatitis.

Supramaximal cholecystokinin displaces Munc18c from the pancreatic acinar basal surface, redirecting apical exocytosis to the basal membrane

“…The progression of Munc18c displacement from the plasma membrane correlated very well with the progression of actin disassembly (Figure 8, e, h, and k), which is well known to occur in this pancreatitis model (30,31). Also, parallel histologic sections obtained from these pancreata demonstrate progressive changes of edematous pancreatitis.…”

“…This cellular location of Munc18c overlaps with the location of syntaxin-4 (Figure 1e) and SNAP-23 ( Figure 1g). F-actin staining with phalloidin ( Figure 1, d, f, and h) is used to define the apical membrane where the actin signal is strongest (30)(31)(32). Taken together, the basolateral plasma membrane of the acinar cell contains a set of t-SNARE proteins capable of forming a fusion complex with the ZG VAMP-2, and Munc18c may be responsible for preventing this complex from forming (15).…”

“…This was performed as we have previously described (30,31). Male Wistar rats (200-250 g) were equipped with an intravenous cannula, followed by the indicated infusion protocols.…”

“…We believe that the Munc18c displacement from the plasma membrane would render the membrane extremely receptive to pathologic exocytosis to occur. The parallel changes of actin disassembly (30,31) would further allow free access of the ZGs to the acinar cell surface (56). Indeed, actin and associated cytoskeletal proteins have been postulated to be involved in physiologic (56) and pathologic exocytoses of the pancreatic acinar cell (30,31).…”

Liver lipid peroxidation and antioxidant capacity in cerulein-induced acute pancreatitis

“…MDA is an indicator of membrane lipid peroxidation. The destruction of the cell membrane structure and damage to cellular organization lead to a disruption in the intracellular transport of digestive enzymes, premature activation of these enzymes and damage to acinar cells (26). It is also possible that the breakdown of capillary permeability caused by oxidative damage is the origin of edema in AP.…”