The osmotic behavior and permeability to non-electrolytes of mitochondria

Abstract

The volume changes of rat liver mitochondria exposed to hypotonic solutions or to solutions of penetrating non-electrolytes were studied by direct estimation of mitochondrial volume from photomicrographs and by changes in optical density of mitochondrial suspensions. The data permit the following conclusions about the osmotic behavior and permeability of these particles. 1. 1. Mitochondria undergo reversible volume changes in anisotonic solutions. 2. 2. Minor secondary changes of undetermined origin also occur. 3. 3. Mitochondria obey osmotic (Boyle-van't Hoff) law. 4. 4. They contain a substantial amount (40–50%) of material which does not participate in volume changes. 5. 5. There appears to be little leakage of osmotically active solute from mitochondria during short exposure to hypotonic solutions. 6. 6. A simple, empirical relation between the optical density of a mitochondrial suspension and mitochondrial volume has been established. 7. 7. Non-electrolytes permeate the mitochondria and thereby induce reversible osmotic volume changes. 8. 8. The rate of penetration is correlated with the olive oil/water partition coefficient of the compound. 9. 9. The permeability constants of the substances studied are quantitatively similar to those found for typical cells. 10. 10. Mitochondria possess a semipermeable membrane which probably contains a high proportion of lipide.