Intracellular compartmentation of Na⁺, K⁺ and Cl^- in the Ehrlich ascites tumor cell: Correlation with the membrane potential

The intracellular distribution of Na⁺, K⁺, Cl^- and water has been studied in the Ehrlich ascites tumor cell. Comparison of the ion and water contents of whole cells with those of cells exposed to La³⁺ and mechanical stress indicated that La³⁺ treatment results in selective damage to the cell membrane and permits evaluation of cytoplasmic and nuclear ion concentrations. The results show that Na⁺ is sequestered within the nucleus, while K⁺ and Cl^- are more highly concentrated in the cell cytoplasm. Reduction of the [Na⁺] of the incubation medium by replacement with K⁺ results in reduced cytoplasmic [Na⁺], increased [Cl^-] and no change in [K⁺]. Nuclear concentrations of these ions are virtually insensitive to the cation composition of the medium. Concomitant measurements of the membrane potential were made. The potential in control cells was -13.7 mV. Reduction of [Na⁺] in the medium caused significant depolarization. The measured potential is describable by the Cl^- equilibrium potential and can be accounted for in terms of cation distributions and permeabilities. The energetic implications of the intracellular compartmentation of ions are discussed.