Roles of magnesium and calcium ions in cell-to-substrate adhesion

The effects of Mg²⁺ and Ca²⁺ ions on cell adhesion to protein-coated Falcon plastic were examined by using fibroblasts from a culture of chicken embryonic sclera. It was found that Mg²⁺ is always more effective than Ca²⁺ in facilitating cell adhesion to the substrates. Cell adhesion is a pH-dependent phenomenon: the cells required Mg²⁺ or Ca²⁺ for attachment to substrates at pH higher than the isoelectric point of the proteins coating a plastic surface, but not at lower pH. With increasing pH from 3.4, cell adhesiveness to substrates decreased up to about pH 5.8. In the presence of Mg²⁺ or Ca²⁺ it increased again above this pH, while in Mg²⁺- and Ca²⁺-free medium it decreased further. Such enhancement of cell adhesiveness with increasing pH corresponded to an increase in the cell's spreading activity due to pseudopodia. Low temperature prevented both cell adhesion and spreading. The cells once attached to substrates in the presence of Mg²⁺ were not detached by EDTA. Cell adhesiveness to substrates was not always raised with increasing concentration of divalent cations, and higher concentration of Ca²⁺ tended to inhibit the initiation of cell attachment. From these results, it was assumed that an enhancement of the cellular spreading activity by divalent cations facilitates cell adhesion to a negatively charged substrate.