The serum dependence of baby hamster kidney cell attachment to a substratum

Normal attachment and spreading of baby hamster kidney cells onto a non-living substratum requires the presence of a specific serum component adsorbed to the substratum surface and Ca²⁺ ions in the medium. In the absence of the adsorbed serum factor or Ca²⁺ ions cells attach but do not spread. Thus, although the initial rate of BHK cell attachment is faster in serum-free medium than serum-containing medium, no cell spreading occurs in serum-free medium. Adsorption of serum onto the substratum results in a lag phase in the time course of cell attachment which can be eliminated by blocking the negatively charged groups of the serum components adsorbed to the substratum surface; blocking positively charged groups or free sulfhydryl groups of the adsorbed serum components is without effect. The requirement for serum components can be substituted for by adsorbing molecules such as concanavalin A or polycationic ferritin to the substratum surface; however, only ConA results in normal morphology of cell spreading. The data are discussed in terms of a non-electrostatic direct cell-substratum binding model of cell attachment.