Intercellular adhesion : I. A quantitative assay for measuring the rate of adhesion

A quantitative procedure for determining the early kinetics of cell aggregation (adhesion) is described. The cells used for this study were obtained by dissociation of 8-day-old embryonic chicken neural retina with crude trypsin. The method is based on determining the decrease in single cells in an aggregating population with the Coulter electronic particle counter. A variety of experiments show that the method is reproducible and capable of detecting relatively small changes in the rate of aggregation. Using a number of criteria, the loss of single cells from the population with increasing time of incubation was shown to result from the formation of aggregates, and not from other phenomena such as cell death or changes in cell permeability. The intercellular adhesions formed under these conditions were stable to mechanical shear and to ethylenediaminetetraacetate, and were partially resistant to crude trypsin. The logarithm10 of the number of single cells in the population was found to be directly related to the time of incubation. The slope of the resultant straight lines could be used as a measure of the rate of aggregation. No lag in aggregation was demonstrable under the standard assay conditions. the rate was affected by the initial cell density, speed of rotation during aggregation, temperature, and by Ca(2+) and Mg(2+). It was not affected by inhibitors of protein synthesis, metabolic inhibitors, ATP, ADP, cyclic-AMP, or horse serum at 37 °C. The quantitative method for determining the initial rate of adhesion should be applicable to studies on the chemistry of this process.