Permeability changes in isolated liver mitochondria during different metabolic states.

The different staining patterns observed in isolated rat liver mitochondria suspended in a negative stain (2.11% ammonium molybdate) that were reported (U. Muscatello, V. Guarriera-Bobyleva, and P. Buffa, 1972, J. Ultrastruct. Res. 40, 235-260) were analyzed with the aim of determining the location of the stain within the mitochondria. The observations made by Muscatello and coworkers on whole, negatively stained mitochondria were confirmed. By embedding the negatively stained mitochondria according to one low denaturation embedding technique, the location of the stain could be determined. In rat liver mitochondria, freshly isolated, the stain was located within wide intracristal spaces. During state 4 respiration, stain was present in the cristae although the two membranes of each cristae were in most cases closely apposed. After 30 sec in state 3 respiration, the stain was present in the matrix, but absent from the cristae. During all three experimental conditions, stain was present in a narrow zone inside the membrane at the surface of the mitochondrion. The changes in permeability leading to an entrance of the stain into the matrix but not the cristae during state 3 respiration, and the reverse situation during state 4 shows that there are two pathways along which the stain can enter the matrix or the cristae. The permeability of these pathways is controlled independently. These observations cannot be explained on the basis of the generally accepted structure of mitochondria. The absence of any other structural modifications and a change in volume of the mitochondria in association with the transition from state 4 to state 3 respiration does not conform with the concept (C. R. Hackenbrock, 1966, J. Cell Biol. 30, 269-297) that the mitochondria undergo extensive "conformational" changes under these conditions.