Freeze-fracture was used to investigate membrane structure in autophagic vacuoles induced in mouse pancreatic acinar cells by injection of neutral red or vinblastine. Early autophagic vacuoles (studied 20 to 60 minutes after drug injection), characterized by the presence of two limiting membranes and numerous segregated membranes, usually appeared in the replicas as typical multilamellar structures. Late vacuoles (studied 4 to 8 hours after drug injection) were identified primarily by their large size and highly irregular shape. The two limiting membranes of autophagic vacuoles, although originating from a common source (the limiting cisternae), were found by freeze-fracture to be distinctly different. The outer membrane always exhibited intramembrane particles on both its fracture faces even though, compared to the membranes of other organelles (endoplasmic reticulum, Golgi complex, and mitochondria), the density (number per unit of area) of these particles was much lower, especially in early vacuoles, and the distribution more heterogeneous. This observation suggests that neither endoplasmic reticulum nor Golgi membranes are the direct source of the autophagic vacuole limiting cisterna, unless a partial loss of particles occurs in these membranes concomitantly with vacuole formation. The inner limiting membrane, as well as the membranes of the segregated organelles, were nearly always totally free of intramembrane particles. This was true even at early time points of the experiment, when in thin sections the trilaminar structure of these membranes was still recognizable. Thus, the loss of intramembrane particles seems to be a very early and rapid event in the process of membrane deterioration occurring inside autophagic vacuoles.
|Number of pages||9|
|Publication status||Published - 1980|
ASJC Scopus subject areas
- Pathology and Forensic Medicine