Sustained contraction (dehydration) of rat liver mitochondria can be readily produced by increasing the tonicity of the outside media, provided Ca++ is removed by EDTA, fatty acids are removed by albumin, and a source of chemical energy (mitochondrial substrate or ATP) is present. This was demonstrated both gravimetrically and turbidimetrically. It was also demonstrated that the net movement of sucrose and H2O under altered conditions of tonicity in mitochondria was dependent on the state of the mitochondria; e.g., in the presence of EDTA, diffusion was blocked, both into and out of mitochondria, whereas, in the presence of EDTA and electron-transport substrates, movement of sucrose and water out of mitochondria was increased. In the presence of Ca++, gramicidin, or fatty acids, diffusion of sucrose into and out of mitochondria is very rapid. Mitochondria obey osmotic law only after Ca++ and fatty acids are removed from them.

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