Intracellular water distribution and aging as examined by X-ray microanalysis.

The results reviewed here demonstrate that 1. the distribution of dry mass as observed in frozen-dried cryosections might be used as an unbiased measure of intracellular dry mass resp. water distributions in the tissue in vivo and 2. the well-known loss of water from cells during aging is solely due to a water loss from mitochondria without changes in the water content of all other components of the cell in the case of rat liver and heart muscle. The reason for the water loss might be increased counter ion binding by membrane-bound enzymes due to decreased fluidity of the inner mitochondrial membrane with aging rather than changes of the permeability of the membrane or chemical modifications of mitochondrial proteins or DNA. It is assumed that the observed changes lead to decreased intramitochondrial diffusion of substrates and to conformational changes of enzymes. This would decrease both the velocity and the binding constants of certain energy-supplying reactions and could therefore play an important role in the aging process.