Heterogeneity of anionic sites at the electrokinetic surfaces of fixed ehrlich ascites tumor cells

Abstract

The net surface negativity of Ehrlich ascites tumor cells was reduced by treatment with neuraminidase and/or ribonuclease. After fixation in glutaraldehyde, the electrophoretic mobilities of the cells were measured, and their average surface charge densities calculated. Fixed cells were also reacted with net positively charged colloidal iron oxide particles, embedded, cut into sections of known approximate thickness, and examined by electron microscopy. Particle counts per unit area of cell surface, which are thought to indicate coulombic binding to cell surface anionic sites, bore no proportional relationship to the surface density of anionic sites calculated from the electrokinetic data. The two sets of data were best “explained” by postulating that the enzyme-sensitive cell surface anionic sites are arranged in higher-than-average density clusters. On average, 30 RNase-susceptible surface anionic sites were covered by one iron particle (c. 8000 Å 2), compared with 20 neuraminidase-susceptible sites. It was also postulated that the anionic sites not susceptible to these two enzymes, were spread more homogeneously over the cellular electrokinetic surface. This model provides a reasonable explanation for the lack of correlation between observed cell social behaviour, and their electrophoretic mobilities, in terms of the heterogeneous distribution of surface ionogenic groups.