Freeze-fracture of membrane fusions during exocytosis in pancreatic B-cells.
To examine the freeze-fracture appearance of membrane alterations at sites of exocytosis in mammalian cells, we studied the secretory granule and plasma membrane of rat pancreatic B-cells during glucose-stimulated insulin secretion. Constant features observed were the scarcity of particles in secretory-granule P-fracture faces and the almost total clearance of intramembranous particles in P-and E fracture faces of the plasma membrane in areas of close apposition of these two membranes preceding fusion; also observed was the temporary persistence of particle-cleared regions after the fusion was completed. Our observations thus support the concept that membranes fuse at sites of closely apposed, particle-free regions and that the physiologically created clear areas found in freeze-fracture replicas of the plasma membrane are the hallmarks of incipient or recent membrane fusion.
D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure; D003594:Cytoplasmic Granules / Q000648:ultrastructure*; D005089:Exocytosis; D005614:Freeze Fracturing; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000502:physiology / Q000648:ultrastructure*; D008566:Membranes / Q000648:ultrastructure; D051381:Rats
D007328:Insulin