The Osmotic Behavior of the Sucrose-inaccessible Space of Mitochondrial Pellets from Rat Liver

Abstract

SUMMARY 1. Parallel measurements were made of the sucrose pcrme- ability and the osmotic behavior of isolated rat liver mitochondria at O-5”. Pellet sucrose spaces and total pellet were de- termined by the isotope dilution method and from pellet water contents, respectively. From these volumes, extraparticulate spaces were derived mathematically. 2. For the case of mitochondria in 0.30 M sucrose, pellet sucrose spaces were 66 to 80% but extraparticulate spaces were only 23 to 33% of total pellet water volumes. Thus about two- thirds of the intramitochondrial water volume is permeable to sucrose. 3. In hypotonic sucrose, all of the mitochondrial space which sucrose does not enter adheres to Boyle-van% Hoff’s Law, be- having as an ideal osmometer. 4. Thus, the apparent contradiction between mitochondrial sucrose permeability and osmotic behavior is considered resolved through study of both the sucrose-accessible and the sucrose- inaccessible space of mitochondrial pellets. Two possible struc- tural bases for this heterogeneity are discussed.