A simple mechanical method for the efficient release of contact inhibition

A method has been devised by means of which a large fraction of cells in a confluent monolayer can be released from contact inhibition of growth and division. This is accomplished without chemical treatment of the cells and in such a way that most cells are provided with free growth area. In essence the procedure involves growing the cells to confluence on surfaces uniformly covered with 200 μ diameter glass beads, which are discarded when confluence has been attained and growth stopped. Removal of the beads dislodges few if any of the cells. After release of inhibition, the cultures double in cell number following the first round of DNA replications, and continue to grow until they are again contact-inhibited. Patterns of incorporation of thymidine, uridine, and amino acids have been examined in inhibited cells and in cells released by this method. The results are in general like those obtained in other systems, but among the few differences are some that indicate a need for re-interpretation of earlier results, obtained with trypsin-treated and serum-stimulated confluent cultures.