Solute movemetns during volume changes in rat-liver mitochondria

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Abstract
The water and solute content of rat-liver mitochondria have been measured during swelling or shrinking of the particles. When mitochondria swell in 0.25 M-sucrose solution there is an increase in the fraction of mitochondrial water penetrated by sucrose. The shrinkage due to transfer of mitochondria from 0.25 M-sucrose to solutions of a higher osmoticity is mainly due to the loss of water from the sucrose-free space. In mitochondria partially permeated by sucrose it is necessary to assume for osmotic equilibrium that the endogenous potassium is solely within a compartment separate from the sucrose. When magnesium or manganese cause a shrinkage of mitochondria there is a loss of potassium that is never greater than that expected from the volume change of the sucrose-free water. When mitochondria have swollen to a state when they contain more than 41. of water/kg of solids they become completely permeable to sucrose and in further swelling the volume changes are due to an uptake of the suspending medium. Below 41. of water/kg of solids the mitochondria are able partially to exclude some components of the medium. Calcium and magnesium have antagonistic effects on mitochondria. Calcium increases the uptake of sodium and increases the loss of potassium, whereas magnesium decreases both these processes. The problems of mitochondrial permeability are discussed.