Probe for polyanionic regions on the cell surface.

The binding of polyuridylate to cells in the presence of proflavine may be used as a probe to provide relative estimates of exposed polyanionic regions on the external surface of the cell. This probe binds preferably to hydrophilic, polyanionic regions, and soluble polysaccharides containing either carboxylate or sulfate groups compete with the binding of this probe. Binding of the probe to protein and lipid regions is considerably weaker. Virus-transformed human fibroblasts bind 10 times less of the probe than nontransformed cells when confluent monolayers are compared. However, as the cell density is decreased, the amount of probe bound per cell increases dramatically both for transformed as well as for normal cells. In fact, human fibroblasts (a) derived from normal donors, (b) from donors with different metabolic disorders, and (c) transformed by simian virus 40, all bind about the same amount of probe when compared at the same density. Populations of human fibroblasts aged in vitro, which contain high proportions of large cells and grow only to relatively low densities in monolayers, bind disproportionately large amounts of the complex.