Polyvalent cations inhibit human neutrophil chemotaxis by interfering with the polymerization of actin

The effect of a series of di- and trivalent cations on the locomotor response of human neutrophils to the chemotactic tripeptide N-formyl-methionyl-leucyl-phenylalanine (FMLP) was investigated. Migration was assessed by the leading front method. The cations inhibited FMLP-stimulated chemotaxis in the rank order: Ni2+ approximately Co2+ greater than Sr2+ greater than Zn2+ greater than Mn2+ approximately La3+ greater than Cd2+ approximately Ba2+ much greater than Mg2+. Benzamil, which blocks Na+/Ca2+ exchange, did not alter chemotaxis by itself but prevented the suppressive effects of each of the polyvalent cations on motility. The ion selectivity sequence and the lack of activity of benzamil are strikingly different than for O(-2) generation, thereby implying different modes of action in the two functional expressions. The F-actin content of the cells was monitored by the fluorescence of rhodamine-phalloidin. Each of the cations displayed comparable efficacy in blocking the polymerization of actin in FMLP-activated cells. Likewise, benzamil exhibited a protective effect, completely overcoming the inhibitory action of the polyvalent cations. The results indicate that these foreign ions gain access to the cell interior via a benzamil-sensitive pathway, namely Na+/Ca2+ exchange. Upon entry into the cytosol, they then interfere with the formation of filaments from actin monomers. These studies help to shed light on the interaction of divalent cations with cytoskeletal and contractile elements in cell motility.