Mechanisms of adhesion among cells of the early chick blastoderm. Role of calcium ions in the adhesion of extraembryonic endoderm cells.

Cells from the extraembryonic endoderm of the gastrulating chick embryo adhere to one another in the absence of divalent cations. The addition of Mg2+ ions to the medium has no effect on the aggregation kinetics but the addition of Ca2+ ions increases the number of cells which aggregate and also stabilizes adhesion. Some aggregation also occurs when cells are suspended in saline devoid of Ca2+ and Mg2+ ions and supplemented with EGTA, a Ca2+ ion complexing agent, but adhesion is not stabilized. Shear sensitive and shear resistant bonds form in Ca-containing as well as in EGTA-containing saline. These results suggest that extraembryonic endoderm cells have Ca2+ indepedent and Ca2+ dependent mechanisms of adhesion.