Different cation requirements for aggregation of BHK cells and their transformed derivatives

BHK21 cells singly dissociated by trypsin aggregate in medium with calcium ions, but not in medium with magnesium ions. Their malignant derivatives (pyBHK) induced by polyoma virus, after dissociation with trypsin, aggregate equally well in medium with either calcium or magnesium ions. When EDTA is used for dissociation of cells from culture on a substrate, neither BHK21 nor pyBHK cells require addition to the medium of divalent cations for rapid aggregation. Trypsin-dissociated BHK21 cells become aggregative in medium without divalent cations, when they are incubated for 60 min in dispersion with medium containing calcium ions before aggregation. In the case of pyBHK cells, incubation in dispersion in the medium with calcium or magnesium ions is effective in this respect. Calcium and magnesium ions are equally effective for adhesion of both BHK21 and pyBHK cells to non-cellular substrate or to a cell monolayer. We discuss the different cation requirements for aggregation of BHK21 and their transformed derivatives in relation to the recovery process of cell surfaces after exposure to trypsin.