Osmotic properties of a proliferating and differentiating line of cells from the bone marrow of the rat.

The effects of cellular differentiation on the osmotic properties of a proliferating line of bone marrow cells has been investigated. This population proliferated and differentiated into distinct maturation phases which have been separated quantitatively by velocity sedimentation at 1g in a Ficoll gradient. Certain osmotic characteristics were evaluated. The volume of osmotically active water increased linearly with maturation. The osmotically inactive volume was variable during proliferation and maturation. Several correlations that concerned the exosmotic movement of water were noted, as follows: 1) membrane permeability to water increased with an increase in the diameter of the nucleus, 2) the ratio of osmotically active water to mean corpuscular volume increased with an increase in the diameter of the nucleus, 3) membrane permeability to water increased with an increase in the osmotically active water normalized to the mean cell volume, and 4) the heat of activation associated with the permeability of the membrane to water increased during maturation and varied inversely with the ratio b/MCV. These results were used to assess the effects of cellular maturation on membrane function and the state of water in a maturing cell population. The permeability data suggest that charged groups on membrane proteins and phospholipids can vary the state of water in the membrane from a thermodynamically mobile state to an "ice-like" state. These unusual properties may be a direct result of a dynamic and functional relationship between cellular water and active biological macromolecules.