The osmotic behavior of the sucrose-inaccessible space of mitochondrial pellets from rat liver.

Although it has been known for more than a decade that the volume of isolated mitochondria is inversely related to the osmolarity of the surrounding medium (2, 3), it was not until 1955 that Tedeschi and Harris (4) demonstrated that mitochondria obey Boyle-van% Hoff’s Law. Since then, supporting evidence for the osmotic behavior of these subcellular structures has been ample (5, 6). In 1957 and 1958, however, it was shown that sucrose, the customary solute for a mitochondrial suspending medium, entered the mitochondria (7-9). In this paper, the results of parallel measurements of mitochondrial sucrose permeability and volume changes are presented. These results offer a resolution to the apparent contradiction that mitochondria behave as osmometers and yet are permeable to sucrose. Whereas the evidence indicates that sucrose does penetrate mitochondria to a certain extent, the space inaccessible to sucrose obeys Boyle-van’t Hoff’s Law, behaving as an ideal osmometer