Electrolyte and non-electrolyte distribution in the Ehrlich ascites tumor cells during the cell cycle

In a previous study, evidence was presented for changes in the state of water and osmotically active solutes during the cell cycle. Total water was constant at 82% (w/w), while the fraction of water that was osmotically active decreased from a maximum during S to a minimum at mitosis. Total Na+, K+, and C1- in milliequivalents per liter of cell water remained constant. Therefore, electrolytes are sequestered in the osmotically inactive water. Evidence is now presented that Na+ exists primarily as one compartment, with a second, slower compartment appearing during S and disappearing during G2. Na+ is completely exchangeable during the entire cell cycle. The distribution of other penetrating solutes was also investigated. When placed in hyperosmotic ethylene glycol solutions, cells first shrink, then swell to their original volumes. 14C-ethylene glycol distributes in 89% of cell water throughout the cell cycle. However, 14C-urea distributes in anywhere from 86-100% of the cell water, depending on the stage in the cell cycle. Both solutes are at chemical equilibrium in water in which they are distributed, but they differ in their effects on cell volume. The final volume at which cells equilibrate in urea varies with the concentration of urea in the environment and with time into the cell cycle. Results suggest a loss of osmotically active particles or decreased osmotic activity of urea.