Mitochondrial translocation in young and old cells.

In most cells, the mitochondria are constantly moving along microtubule chains. This paper proposes the hypothesis that the mitochondrion is directed to locations in the cytoplasm rich in nutrition (pyruvate, lipid droplets) by fluid movements within the cytosol that are induced by local differences in osmotic pressure. When the mitochondrion absorbs pyruvate and phosphate, the osmotic pressure decreases and becomes lower than in other locations. In old cells, part of the volume is excluded to the mitochondria by accumulated cross-linked proteins. When the mitochondria are fixed, as in striated muscle, the metabolic exchange may be confined to diffusion of the metabolites.