The relation between surface area and anchorage dependence of growth in hamster and mouse fibroblasts

Abstract

Anchorage dependence can be defined as an increase in proliferation which is seen when cells are allowed to attach to a solid surface. We have measured this increase by time-lapse cinematography and other methods, and have compared it with measurements of the change in surface area which also occurs. Anchorage dependence can be varied over very wide limits in cells of the NIL-8 hamster fibroblast line by varying the concentration of serum in the medium. Thus in a concentration of 5% serum, the transition probability (a measure of growth rate) of attached cells is 8 times greater than in suspension. When the serum concentration is raised to 66%, attached and suspended cells grow at the same rate. We have found that this change in growth is accompanied by a corresponding change in the exposed surface area of the cells. Thus in 5% serum, the area of attached is 3 times greater than suspended cells, while in 66% serum, the areas of attached and suspended cells are equal. There is also a significant relationship between the area and the total amount of growth achieved, since both suspended colonies and attached confluent monolayers appear to stop growing at the same surface: volume ratio. Several aspects of this relationship between anchorage dependence and area are also seen when other different types of cell are cultured in the suspended and attached state, all at the same serum concentration. These experiments show that change in exposed surface area can provide a complete explanation for the anchorage dependence of NIL-8 cells and suggest the possibility that this might also be true of animal cells in general.