EXAMINATION BY FLUORESCENCE AND EPR SPECTROSCOPY OF THE STATE OF MITOCHONDRIAL AND LYSOSOMAL MEMBRANES UPON FREEZE THAWING

The results of spectroscopic examination of mitochondria and lysosomes indicate that freeze-thawing leads to alterations of different character and extent in membrane structural organization which manifest as changes in the molecular packing of the organelle membrane lipid bilayer, lateral separation of lipids into individual domains, and impairment of membrane permeability. Supercooling of organelle suspensions without crystallization of external water has been found not to affect membrane barrier function markedly; however, such a decrease in the temperature results in a slight loosening of the membrane with an increase in the volume of subcellular structures. The crystallization of external water causes dehydration of organelles, which favors a decrease in their volume, increasing the viscosity of the liquid phase inside subcellular structures and packing the lipid bilayer. Changes in the permeability of mitochondrial and lysosomal membranes manifest during thawing after the formation of an external liquid phase and might be due to the sharp rehydration of these membranes through latent membrane defects formed upon freezing. © 1990.