Reversible inhibition of cellular aggregation by cytochalasin B and colcemid

Aggregation of normal mouse fibroblast-like cells, placed on the surface of a Millipore filter, was investigated quantitatively. The addition of 10 μg/ml of cytochalasin B (a substance blocking active cell movements) or 0.1 μg/ml of colcemid (a substance disturbing polarization processes in cells and, consequently, interfering with directional cell movements) completely inhibits such aggregation. The inhibition is reversible—after removal of the agents the cells again aggregate. It is concluded that aggregation of cells in this experimental system requires active cell movement and cellular polarization.