The role of G-proteins in the activation of human leukocytes by particulate stimuli to produce reactive oxygen metabolites

Abstract

Effects of pertussis toxin (PTX), cholera toxin (CTX) and an anhydrolyzable GTP analogue, GTPγS, on the levels of free intracellular calcium ([Ca 2+] i) and the production of reactive oxygen metabolites (ROM) in human polymorphonuclear leukocytes (PMNL) were studied during cell activation. Cells were stimulated by particulate stimuli, quartz or chrysotile, and soluble stimuli, formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol myristate acetate (PMA). Pretreatment of PMNL with PTX decreased fMLP-induced elevations of [Ca 2+] i but not those induced by quartz or chrysotile. CTX, in turn, decreased both quartz- and fMLP-induced elevations of [Ca 2+] i. Likewise, PTX inhibited only fMLP-induced production of ROM, whereas CTX inhibited also those induced by quartz, chrysotile or fMLP. PTX or CTX did not, however, have an impact on PMA-induced production of ROM. GTPγS alone did not elevate [Ca 2+] i or amplify fMLP-, quartz- or chrysotile-induced [Ca 2+] i elevation. However, GTPγS alone increased the production of ROM and amplified ROM production induced by fMLP and quartz. The present results suggest that a CTX-sensitive G-protein may be involved in quartz-induced PMNL activation whereas an fMLP-induced neutrophil activation may be regulated by G-proteins sensitive to both PTX and CTX. The involvement of G-protein in chrysotile-induced leukocyte activation is not likely. There may be, however, a relationship between G-protein-mediated cell signalling and quartz-induced production of reactive oxygen metabolites in these cells.