Electrometric Determination of Surface Charge of Cultured Mammalian Cells ∗

Summary

By means of an electrometric method, surface charge density was measured in rabbit, myocardial cells and mouse lung cells. As the pH was varied from 7.4 to 2.2, changes in the surface charge yielded a titration curve of the surface colloids. The isoelectric point of each surface is close to pH 2.2, and most of the titratable groups occur between pH 2.2 and 3.7. Net negative charges of 0.066 equivalents (myocardial cells) and 0.060 equivalents (lung fibroblasts) are found at pH 7.4 Bivalent cations, Ca and Mg, lower the negative charge through binding and electrostatic interactions. Incubation of myocardial cells with trypsin also diminishes the density of titratable groups. Interactions of cells with each other and with other organisms, macromolecules, and electrolytes are determined by the physicochemical properties of the amphoteric surface colloids.