Studies on contract inhibition of growth in the mouse fibroblast, 3T3. I. Changes in cell size and composition during 'unrestricted' growth.

Growth of the contact-inhibited 3T3 and its SV40-transformed derivative, 3T3T is unbalanced. Despite obvious exponential increase in cell number, cell volume, RNA and protein show a marked decrease with increasing population density in both cell types, greater in 3T3 than 3T3T. Daily medium change does not correct this growth pattern but merely seems to equalize initial growth rates of the 2 cell types and prolong the period during which the cell number continues to increase. The evidence suggests that the lag period that ensues following plating of the cells is a period of intense metabolic activity during which a large proportion of cellular protein and RNA is synthesized in preparation for exponential growth.