Affiliations: [a] Humboldt University, Department of Biology, Division of Biophysics, Invalidenstrasse 42, Berlin 1040, G.D.R. | [b] A.N. Frumkin Institute of the USSR Academy of Sciences, Leninskij Prospekt 31, 117071 Moscow, U.S.S.R. | [c] Friedrich Schiller University, Medical Faculty, Department of Electron Microscopy, Ziegelmühlenweg 1, Jena 6900, G.D.R.
Note: [] Accepted by: Editor D. Lerche
Abstract: We present a model for the calculation of intragranular vesicle adhesion energy in a two-vesicle system consisting of an external secretory vesicle (chromaffin granule) and an intragranular vesicle (IGV) that adheres from the inside to the granule membrane. The geometrical parameters characterizing the granule-IGV systems were derived from freeze-fracture electron micrographs. Adhesion is brought about by incubation of the granules in hyperosmolar sucrose solutions. It is accompanied by a deformation of the granule because the intragranular vesicle bulges it outwards, and by segregation of intramembraneous particles from the adherent part of the granule membrane. Adhesion prevents the deformed granules from osmotic re-expansion and, therefore, causes hyperosmotic relaxation lysis. We estimated specific adhesion energy at −3 erg/cm2, a value which is 10–1000 times larger than the energy of van der Waals interaction between membranes. This large interaction energy probably results from changes of the granule core induced by dehydration. A minimization of the interface between the granule core and adjacent membranes could exclude intragranular vesicles from the core and squeeze them towards the granule membrane. This might induce a new kind of interaction between both membranes, which is irreversible and causes lysis upon osmotic relaxation.
