Local starvation for epidermal growth factor cannot explain density-dependent inhibition of normal human glial cells

Mouse epidermal growth factor (mEGF) is a potent growth promoter of human glial cells in sparse cultures, whereas very little stimulation of growth in dense cultures is induced by the factor. In the present communication, the possibility that the density-dependent inhibition is caused by a reduced binding/uptake of the factor was scrutinized. It was found that the number of mEGF binding sites was 20,000 and 35,000 per cell in sparse and dense cultures, respectively. The dissociation constant of the binding reaction was not influenced by the cell density. It was concluded that crowded cells are not starved for the factor and that a decrease in number or affinity of the EGF receptors can be excluded as a cause of the inhibition.