Membrane fusion events during endocytosis in mouse kidney tubule cells detected by rapid freezing followed by freeze-substitution.
Membrane fusion events during endocytosis were examined in renal proximal tubule cells processed by rapid freezing followed by freeze-substitution. An extensive fusion site of the membranes between two apical vacuoles or a vacuole and a lysosome, which appeared as a pentalaminar structure, was not observed in this study, though such a pentalaminar structure has been found in chemically fixed specimens. In vitro experiments using subcellular fractions revealed that the pentalaminar structure did not always represent the initial stage of membrane fusion. Membrane fusion appeared to occur in a specific membrane site, wHere a minute pore connecting the two lumens was formed immediately after the two membranes came into contact with each other. Some pore necks showed an asymmetrical feature which consisted of a sharp corner and a gently curved corner. Enlargement of the pore appears to be mediated by a fibrous structure observed near the sharp corner of the pore neck.
Fujioka
A
A
Department of Anatomy, Kinki University School of Medicine, Osaka, Japan.
Ohtsuki
M
M
Nagano
M
M
Mori
S
S
D000818:Animals; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D002642:Chick Embryo; D015925:Cryopreservation / Q000379:methods; D004705:Endocytosis / Q000502:physiology*; D006651:Histocytochemistry / Q000379:methods; D006735:Horseradish Peroxidase; D007684:Kidney Tubules / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D008297:Male; D008561:Membrane Fusion / Q000502:physiology*; D051379:Mice; D008854:Microscopy, Electron / Q000379:methods; D015388:Organelles / Q000502:physiology / Q000648:ultrastructure
D006735:Horseradish Peroxidase