Preservation of Biomembranes by High Pressure Freezing ?

Abstract

Sample preparation techniques for electron-microscopy (EM) dictate our perception of the microworld: any structural information which is lost or distorted during preparation can not be regenerated later and might lead to wrong interpretation of the observed micrograph.Cryofixation based procedures for specimen preparation can avoid most of the structural alterations associated with standard techniques based on chemical fixation. The ultrastructure can be represented in a near “native state” thanks to the high time resolution for dynamic cellular events (1).High pressure freezing (2) permits to cryoimmobilize biological samples up to approx. 200μm thick, in contrast to rapid freezing procedures at ambient pressure that are useful to cryoimmobilize samples up to 10-20 μm thick. The actual samplethickness that can be adequately frozen (=without visible damage due to ice crystal formation in freeze-substituted or freeze-fractured specimens) depends on the concentration of naturally occuring substances that exhibit cryoprotective activities.