The Biological Action of Ions and the Concentration of Ions at Surfaces

1. It is pointed out that at the surface of a cell the absolute concentration of ions, and the ratios of the concentrations of the individual ions, are usually different from the corresponding quantities in the environmental fluid. It is suggested that the necessity for a Na:Ca ratio of the order of 50:1 in a physiologically balanced fluid is found because such a ratio in the environmental fluid produces a Na:Ca ratio of the order of unity at the cell surface. 2. The concentrations of calcium and sodium ions at the surface of ovalbumin molecules are calculated. It is shown that calcium is bound (a) by electrostatic forces, (b) by formation of apparently unionized complexes with carboxyl groups. The complex formation obeys the law of mass action. 3. The ratio, total Na:total Ca at the surface of various cells in physiological media is calculated from the electrokinetic potentials of the cells. The calculated ratio is of the order of unity. In two cases calculation of the maximum possible total Ca at the cell surface by two other independent methods gives values of the same order of magnitude as the calculation from electrokinetic potentials. 4. It is shown that, where the toxic action of ions is due to complex formation with anions present at a surface, the logarithms of the equitoxic concentrations of the metals should be a linear function of the standard electrode potentials of the metals. 5. Calculations show that the concentration of colloidal Fe at the surface of organisms in sea-water should be far greater than the concentration in the environment: it is suggested that marine plants derive their iron from this layer of adsorbed colloidal iron. 6. A mechanism is suggested which provides for intense adsorption of drugs at specific surfaces.