TIME-COURSE OF VINBLASTINE-INDUCED AUTOPHAGOCYTOSIS AND CHANGES IN THE ENDOPLASMIC-RETICULUM IN MURINE PANCREATIC ACINAR-CELLS - A MORPHOMETRIC AND BIOCHEMICAL-STUDY

The time course of the vinblastine(-sulfate 10 mg/kg body weight, sing le injection)-induced enlargement and subsequent regression of the aut olysosomal compartment was studied by electron microscopic morphometri cal and cell biochemical methods in order to gain information concerni ng some key problems of this major route of intralysosomal degradation of the cell's endogenous macromolecules and structures, Detailed anal ysis of the dynamics of the total autophagic vacuole (AV) compartment and its different subcompartments (early, advanced, late, and fused AV s), as well as of changes of rough-surfaced endoplasmic reticulum (RER ) showed: 1. Pancreatic acinar cells react to vinblastine biphasically , i.e. two expansion phases of the AV compartment, the first in the ii to 90 min and the second in the 2 to 8 h post-injectional periods, we re detected, 2. Fusions of AVs are not inhibited by vinblastine, at le ast during the second expansion phase when cytoplasmic volume fraction (CVF) of fused AVs steadily increased until the 12th h, Fusion of ear ly, advanced and late AVs or composition of fused complex vacuoles (AV (c)) are somehow regulated, as the proportion of the three AV stages f rom the CVF of AV(c) was maintained constant throughout the second exp ansion phase. 3. Stimulation of autophagosome formation and resulting substrate overload seems to be the primary mode of action by which vin blastine causes the enormous expansion of the autolysosomal compartmen t. 4. Degranulation of the rough-surfaced endoplasmic reticulum (RER) membranes occurs in a biphasic fashion, similarly to the volume and su rface changes of the AV compartment, thus supporting our previous hypo thesis, that labilization or change of RER may have a role in the form ation of autophagosomes. 5. Vinblastine-induced autophagocytosis is a selective process, as mitochondria, Golgi elements and zymogen granule s are very much underrepresented, whereas RER is more than twice overr epresented in the volume of early AVs, when compared to their volume f raction in the whole cytoplasm. 6. Immunogold electron microscopy reve aled the presence of ubiquitinylated proteins in advanced and late, bu t not in early AVs.