Inhibition of enzyme secretion and autophagy of secretory granules caused by action of high concentration of secretory hormones on rat pancreatic slices

The actin-myosin cytoskeleton mediates reversible agonist-induced membrane blebbing

Suprastimulation of pancreatic acinar cells with specific agonists inhibits zymogen secretion and induces the formation of large basolateral blebs. Currently the molecular mechanisms that mediate this dramatic morphologic response are undefined. Further, it is unclear if blebbing represents a terminal or reversible event. Using computer-enhanced video microscopy of living acini we have found that these large blebs form rapidly (within 2–3 minutes) and exhibit ameboid undulations. They are induced by small increases in agonist concentration and require an energy-dependent phosphorylation event. Remarkably, the blebs are rapidly absorbed when agonist levels are reduced, indicating that blebbing is a reversible response to a physiological stimulus, not a terminal event. Morphological methods show that these dramatic changes in cell shape are accompanied by a marked reorganization of actin and myosin II at the basolateral domain. During 30 minutes of suprastimulation, both basolateral actin and myosin II gradually increase to form a ring centered at the necks of the blebs. Immunocytochemical and biochemical studies with a phospho-specific antibody to the myosin regulatory light chain reveal an activation of myosin II in suprastimulated acini that is completely absent in resting cells. Studies using cytoskeletal antagonistic drugs indicate that bleb formation and motility require actin remodeling concomitant with an activation of myosin II. This aberrant activation and reorganization of the actin-myosin cytoskeleton is likely to have detrimental effects on acinar cell function. Additionally, this mechanism of bleb formation may be conserved among other forms of physiological blebbing events.

Perifusion of isolated rat pancreatic acini: carbamylcholine-induced biphasic amylase release

To solve many problems in other in-vitro methods such as perfusion and static incubation, perifusion of isolated rat pancreatic acini was established. Continuous stimulation by carbamylcholine induced a biphasic secretory response, a sharp initial phase and a slow-varying second phase. The junction of these two phases occurred at almost the same time (in about 7 min of stimulation) at any concentration of carbamylcholine. The slow-rising former part of a second phase indicated that a biphasic pattern is produced by overlapping of two kinds of real phases and the beginning of a real second phase occurs at the time of the junction. The concentration dependence of amylase release showed a bell-shaped pattern and the maximal amylase release at an optimal concentration (10(-6)M) was 5.43 +/- 0.24% total/30 min. The sustained latter part of a second phase showed a slow decline at optimal or less concentrations but a plateau at supraoptimal concentrations.