Cell cycle and cell protein content of Chinese hamster cells grown in culture with daily renewal of medium

Microspectrophotometric and autoradiographic procedures were used to determine cell protein content and cell cycle parameters of Chinese hamster V79 cells growing as monolayer cultures with daily renewal of medium. The frequency of G 1 cells decreased and then increased as the cultures grew. Cell size at mitosis and at the G 1/S boundary changed only slightly during growth. The changes were very similar to those reported earlier for cultures of the same cell line grown without renewal of medium, but changes in the frequency of G 1 were somewhat slower and those in cell size were much less marked when the medium was renewed daily. The results of the two studies taken together show that cell cycle parameters and cell size change even during periods of exponential growth, and that daily renewal of medium slows but does not prevent the changes. Both studies show that the onset of DNA synthesis is more sensitive to conditions in older cultures than is the onset of mitosis. Our results indicate that radiation from incorporated isotopes might seriously affect the results of the labeled mitoses method of cell cycle analysis, especially when cell crowding is involved.