[Ca2+]i-transients and actin polymerization in human neutrophils under stimulation with GRO alpha and complement fragment C5a.

The neutrophil chemotaxins, complement fragment C5a (C5a) and GRO alpha, induced the mobilization of Ca2+ from intracellular stores and the polymerization of actin in human neutrophils as assayed by flow cytometric measurements. [Ca2+]i-transients developed as an "all-or-none" response. Individual neutrophils required different threshold concentrations of added ligand to induce [Ca2+]i-transients which were then always maximal. In contrast, chemotaxin-induced formation of actin filaments in single neutrophils occurred in a dose-dependent manner. Pertussis toxin blocked chemotaxin-induced actin polymerization and [Ca2+]i-transients indicating that both cell responses shared initial activation steps such as ligand binding and activation of guanine nucleotide-binding proteins (G-proteins).