Changes of total water and sucrose space accompanying induced ion uptake or phosphate swelling of rat liver mitochondria

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Abstract
1. Total water exchangeable with tritiated water and sucrose space were measured in rat liver mitochondria during the uptake of K+ induced by valinomycin and the release caused by nigericin. The K+ content and the sucrose-inaccessible water rose and fell together. 2. Swelling resulting from phosphate addition in a medium of high K+ concentration was associated mainly with increased sucrose-accessible water, which carried dissolved K+. This change was reversed by addition of ATP. 3. The response of the sucrose-inaccessible space to changed osmolarity was qualitatively that expected if the mitochondrial K+ is assumed to be present in this space with a univalent anion. 4. It is brought out that the light-scattering method fails to distinguish between changes in sucrose space and in sucrose-inaccessible space, which in the present experiments could be altered respectively by phosphate (in high K+ solution) and by cation uptake induced by antibiotic.