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Abstract:
Different membrane preparations of the fragmented sarcoplasmic reticulum (FSR) were examined by means of the electron microscope 1. after freeze-drying, 2. after partial dehydration and 3. after standard dehydration and embedding. Prior to these comparative preparational procedures the isolated membranes were either left in their native state or incubated with Hg-phenyl azoferritin or delipidated by digestion with phospholipase A and washing with albumin.
The freeze-drying technique yielded satisfactory results only when fixation was carried out with OsO4 vapour after accomplishing the drying. Even then, good preservation of the vesicular and membrane structure could—if at all—only be obtained in the very surface area of the pellet droplets, maximally up to a depth of 2–3 μm.
The average vesicle diameter of freeze-dried sarcoplasmic membranes measures slightly less than that of chemically dehydrated membranes, particularly clearly demonstrated in delipidated preparations. The membrane structure itself, however, is thicker in freeze-dried than in chemically dried material. A peculiarity of freeze-dried untreated and ferritin incubated membranes is that the usually light inner layer of the unit membrane is comparatively darker than in the corresponding chemically dehydrated preparations and than in all delipidated preparations, thus giving rise to a more compact membrane appearance of these freeze-dried FSR vesicles.
While in sections of ferritin decorated, chemically dehydrated preparations the ferritin particles are arranged like a chain of pearls outside around the membrane, the ferritin particles are located in freeze-dried material immediately on the outer dense line of the vesicular membrane.
