Calcium‐Dependent and Calcium‐Independent Adhesive Mechanisms Are Present During Initial Binding Events of Neural Retina Cells

The hypothesis that intercellular adhesion can be subdivided into two separable phenomena, an initial recognition event and a subsequent stabilization, is supported by the use of a new cell binding assay that provides a quantitative measure of intercellular binding strengths. Radioactive single cells are brought into contact with cell monolayers at 4 degrees C in sealed compartments. The compartments are inverted and a centrifugal force is then applied tending to dislodge the probe cells from the monolayers. By varying the speed of centrifugation, the force maintaining association between embryonic chick neural retina cells was determined to be on the order of 10(-5) dynes after incubation at 4 degrees C. Brief incubations at 37 degrees C resulted in significant strengthening of the intercellular bond. Using this cell binding assay, neural retina cells were shown to exhibit both a Ca++-independent and a Ca++-dependent mechanism in their initial binding to one another.