Vinblastine-induced autophagic vacuoles in mouse liver and Ehrlich ascites tumor cells as assessed by freeze-fracture electron microscopy.

The structure of the membrane limiting apparently newly formed autophagic vacuoles was studied in vinblastine (VBL) induced autophagocytosis in mouse liver parenchymal cells and in Ehrlich ascites tumor cells. In the VBL-treated cells, the formation of autophagic vacuoles was far greater than in the controls as examined by thin section transmission electron microscopy. In freeze-fracture studies of both VBL-treated and control cells, only the P- and E-fracture faces of the outer limiting membrane of the autophagic vacuoles contained a few intramembrane particles (IMP). Their density appeared however, to be much lower than the IMP density on the P- and E-fracture faces of the endoplasmic reticulum or of the Golgi apparatus. The inner limiting membrane of the autophagic vacuoles was smooth. It is apparent that the membranes of endoplasmic reticulum or Golgi apparatus are not directly involved in autophagic vacuole formation.