title: G protein threshold behavior in the human neutrophil oxidant response: measurement of G proteins available for signaling in responding and nonresponding subpopulations.
abstract: Threshold behavior is an important aspect of signal transduction pathways that allows for responses to be turned on or off. Human neutrophil responses to N-formyl peptides, including oxidant production and release, exhibit threshold behavior with respect to the number of G proteins available for signaling; progressive treatment of neutrophils with pertussis toxin causes the conversion of responding cells to nonresponding cells. To quantify the threshold level of G proteins required for signaling of N-formyl peptide stimulated oxidant production in a neutrophil population, we used a plasma membrane associated G protein quantification assay in conjunction with a sorting flow cytometer and measured differences in the average number of G proteins available for signaling per cell in both the responding and the nonresponding subpopulations after pertussis toxin treatment. Although there appeared to be a threshold separating responding cells and nonresponding cells for a given sample, no discrete threshold was measured across multiple treatment conditions. A mathematical model of the early steps in signaling suggests that cell-to-cell variability in signal parameters, such as numbers of signal components and values of kinetic rate constants, obscures the measurement of a discrete threshold and leads to an apparent decrease in the threshold level of G proteins available for signaling as the total G proteins are decreased.
authors.affiliation: Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Peter S
authors.initials: PS
authors.lastname: Chang
authors.forename: Daniel
authors.initials: D
authors.lastname: Axelrod
authors.forename: Geneva M
authors.initials: GM
authors.lastname: Omann
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Linderman
mesh_terms: D002469:Cell Separation; D005434:Flow Cytometry; D020962:Heterotrimeric GTP-Binding Proteins / Q000032:analysis*; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000737:chemistry / Q000145:classification / Q000378:metabolism*; D016877:Oxidants / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D016877:Oxidants; D009240:N-Formylmethionine Leucyl-Phenylalanine; D020962:Heterotrimeric GTP-Binding Proteins