The subapical actin cytoskeleton regulates secretion and membrane retrieval in pancreatic acinar cells.

We examined the effects of disruption of the actin cytoskeleton by cytochalasin D (cytoD) on basal and carbamylcholine-stimulated exocytosis and on compensatory membrane retrieval in pancreatic acinar cells. Although the involvement of actin in exocytosis is reasonably well established, its role in these coupled processes is not understood. Our findings suggested that cytoD inhibited stimulated secretion of amylase.

Rab4 associates with the actin terminal web in developing rat pancreatic acinar cells.

Rab4 is a small GTP-binding protein that has been implicated in the regulation of membrane traffic and recycling of transferrin receptors and GLUT4 transporters along the endocytic pathway. Here we present data that suggest a novel and very different role for rab4 during development in the rat exocrine pancreas. On immunoblots of pancreatic homogenates, a dramatic increase in rab4 expression occurred over the first 40 h after birth, concomitant with the time of acquisition of stimulus-secretion coupling.

The expression pattern of rab3D in the developing rat exocrine pancreas coincides with the acquisition of regulated exocytosis.

Although the secretory apparatus of rat pancreatic acinar cells already has a mature appearance in late stage fetuses, the regulated exocytotic pathway becomes functional only after birth. In this study we tested the hypothesis that the acquisition of stimulus-secretion coupling in the acinar cells depends on the developmental expression of rab3D, a small GTP-binding protein which we have previously shown to be associated with zymogen granule membranes in the adult pancreatic acinar cell. On immunoblots of pancreatic homogenates, rab3D became detectable on gestational day 18.

Localization of cellubrevin to the Golgi complex in pancreatic acinar cells.

Cellubrevin is the smallest (14 kDa) isoform of the synaptobrevin (VAMP) protein family and is found in a wide variety of tissues. Western blot analysis with a polyclonal antibody against the unique N-terminus of cellubrevin identified a protein of 14 kDa in rat pancreas. This protein distributed predominantly to the particulate fractions from the rat exocrine pancreas and was totally resistant to NaHCO3 washes, indicating that it is an integral membrane protein.

Rab3D localizes to secretory granules in rat pancreatic acinar cells.

This study reports of presence of rab3D, a low M(r) GTP-binding protein, in rat pancreatic acinar cells and islets using a combination of Western blot analysis, two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis/isoelectric focusing, and light and electron microscopic immunocytochemistry. For these purposes, we used an affinity-purified rabbit polyclonal antibody generated against the exclusive amino terminus of rab3D. Failure to detect rab3A, B or C in pancreatic acinar cells with their respective antisera indicated that the rab3D immunoreactivity was not due to cross-reaction with rab3A, B or C.