Electrochemical State of Potassium and Sodium in Free Cells of Acer pseudoplatanus

The intracellular distribution of K⁺ and Na⁺ ions has been determined by compartmental analysis of isotope exchange. The simultaneous measurement of electrical potentials allowed us to show that the distribution of K⁺ was close to thermodynamic equilibrium while the internal concentration of Na⁺ was well below the value predicted for the equilibrium. The efflux of Na⁺ was more sensitive to temperature than its influx. Both ouabain and variations in the external levels of KCl produced weak and inconsistent effects, observations which would emphasize the difference between the Na⁺ extrusion mechanism of plants and animals. The Na⁺ extrusion system of Acer cells ceased to be functional in Na⁺-depleted cells but recovered its function if the cells were placed in 10 mM NaCl, which suggests that the extrusion system was induced by the level of internal Na⁺ ions.