Permeability to water, dimension of surface, and structural changes during swelling in rat liver mitochondria

Rates and amounts of water translocation across the mitochondrial membrane have been studied with a photometric technique. The process of water translocation can be described in terms of the diffusion equations, and the mitochondria behave as spherical bodies between 15 and 110 mosm. A permeability coefficient to water of 5.3×10(-3)cm sec(-1) has been calculated. The mitochondrial surface is about 1m(2)/g protein during incubation in 0.10M KCl, and increases to 30 m(2)/g protein during incubation in 0.005M KCl.The osmotic shrinkage of hypotonically swollen mitochondria has also been studied. Complete reversibility of hypotonic swelling occurs only after incubation of mitochondria in media below 60 to 90 mosm. The appearance of the reversibility is phenomenologically correlated with the rupture of the outer mitochondrial membrane., Below 30 mosm there is a change of the absorbance properties of the membrane. The change correlates with the complete unfolding of the cristae and is attributed to ultrastructural reorganization of the membrane following mechanical stretching.