Two Mechanisms in Cell Adhesion Revealed by Effects of Divalent Cations

The effect of divalent cations on cell-to-cell and cell-to-substrate adhesions was studied using two different types of chicken embryonic cells (fibroblastic and neural retina cells). Mn2+, Co2+, Mg2+ and Ca2+ were effective in promoting the aggregation of fibroblastic cells, while Sr2+ and Ba2+ were not effective. Among these ions, Ca2+ showed some unique effects on cell aggregation. Aggregation was initiated immediately after the addition of Mn2+, Co2+ or Mg2+ whereas with Ca2+ a lag period was always observed. When the medium contained both Ca2+ and Mg2+, the aggregate size formed was bigger than that formed with either ion at an equimolar concentration. The divalent cation dependence of fibroblastic cell adhesion to non-cellular substrate was essentially the same as that of cell-to-cell adhesion. The aggregation of neural retina cells specifically depended on the presence of Ca2+. For adhesion of neural retina cells to non-cellular substrate, however, Ca2+ was not effective, and only Mn2+ or Co2+ was effective. These results suggest two different mechanisms in cell adhesion.