Role of particle electrostatic charge in adhesion and ingestion in Dictyostelium discoideum amoeboid cells.

The use of colloid iron hydroxide, Alcian Blue and enzymic treatments confirmed that the negative charges of Dictyostelium discoideum cell surface are mostly due to carboxylic groups. The role of electrostatic charges in adhesion and ingestion was determined by exposing cells to untreated latex beads, polylysine or polyglutamic-acid-coated beads, or carboxylated beads. This study showed that negatively charged beads presented a weaker adhesion strength than positively charged ones and that adhesion was strongest with untreated beads. This shows that hydrophobic forces are stronger than those induced by opposite electric charges between particle and cell surface. The ingestion rate was not directly related to adhesion because negatively charged beads presented the highest phagocytic rate, polylysine-coated beads had the lowest and neutral beads an intermediate one. The treatment of cells with polylysine or polyglutamic acid before neutral bead addition generally enhanced the ingestion rate. Electron microscopic observations made on polylysine-treated cells showed, however, that this stimulating effect was not due to the presence of the polymer on the cell surface but to a membrane clearance phenomenon occurring during polymer elimination. All these observations have led to the conclusion that the electric charges of the particle do not play a major role in D. discoideum phagocytic ability. Hydrophobic forces and probably other unknown parameters related to the cell surface properties are more important.