Stimulating the proliferation of quiescent 3T3 fibroblasts by peptide growth factors or by agents which elevate cellular cyclic AMP level has opposite effects on motility.

The effects of some chemically defined growth factors on the locomotion of quiescent Swiss 3T3 fibroblasts have been studied. A computer digitiser has been used to facilitate recording the paths followed by cells in time-lapse films; this method allows 500 cell-hours to be recorded in 1 h of real time. Individual cells in the same culture vary widely in speed. This variation is not associated with the positions of the cells in the cell cycle; a small deceleration which seems to occur in G2 cannot account for any significant part of the variation seen. Nor is it related to the time elapsing before the cell divides, although this is equally variable; the speed and age at division of particular cells appear to be entirely independent of one another. Nevertheless, good reproducibility is seen between the mean speeds of large numbers of cells from the same type of culture. The mean speed of quiescent cells is less than 2 microns/h. A mixture of epidermal growth factor (EGF) and vasopressin, in the presence of insulin, is known to be a potent promoter of proliferation in this system. We have found it to increase speed to 30 microns/h. Agents which stimulate the cellular level of cAMP are also known to be potent promoters of proliferation in the presence of insulin. We have found these agents to be inhibitors of locomotion; several cycles of cell division take place while the cells move at a speed no greater than that seen in the presence of cytochalasin B (CB) or colchicine. These findings therefore give further support to the idea that there may be two different classes of growth-promoting factors, with major differences in their mode of action. They show that some members of these two different classes have opposite effects on motility.