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ph, serum and Zn++ in the regulation of DNA synthesis in cultures of chick embryo cells

Variations in pH, serum concentration and the availability of Zn++ in the medium markedly influence the initiation of DNA synthesis in cultured chick embryo cells. This report considers the interplay of these factors with one another and with other factors such as type of medium, cell population density and the malignaut transformation in an attempt to better define the variables of the growth control system. Conditioned medium seems to protect the cells against the inhibitory effects of lowered pH. Increased serum concentration has a similar, but more striking effect. Increased serum concentration and pH, as well as decreased population density, which stimulate DNA synthesis, also lower the sensitivity of DNA synthesis to inhibition by Zn++ deprivation. Likewise, cell transformation by infection with Rous sarcoma virus lowers the sensitivity of DNA synthesis to inhibition by Zn++ deprivation and by pH reduction. The response of DNA synthesis to pH varies with the type and concentration of buffer used. It is concluded that there are a number of mutually interacting variables involved in the regulation of animal cell multiplication.