Stimulation of human polymorphonuclear leukocytes by consecutive doses of quartz and interactions of quartz with fMLP

The role of free intracellular calcium [Ca2+]i was studied in the production of reactive oxygen metabolites (ROM) by human polymorphonuclear leukocytes (PMNL) after a single or two repeated doses of quartz. The significance of [Ca2+]i in the production of ROM was also studied after a dose of quartz prior to, or after, a dose of formylmethionylleucylphenylalanine (fMLP). When the production of ROM and changes in [Ca2+]i were measured after repeated stimulations of cells, the cells were always washed between stimulations. A dose of quartz elevated [Ca2+]i in untreated and washed cells, whereas a second dose of quartz did not induce any further increase in [Ca2+]i. On the contrary, quartz stimulated ROM production after both one and two consecutive doses. fMLP alone elevated [Ca2+]i and increased the production of ROM. Quartz before fMLP did not modify fMLP-induced [Ca2+]i increase, but attenuated fMLP-induced ROM production. Quartz-induced elevation of [Ca2+]i was not affected by a prior dose of fMLP, but the production of ROM by quartz was greatly amplified by prior exposure of PMNL to fMLP. Thus, both quartz and fMLP increase the production of ROM by mechanisms in which [Ca2+]i may have a key role. Priming of PMNL with fMLP prior to quartz seems to amplify quartz-induced ROM production but not to affect [Ca2+]i. It is plausible that both [Ca2+]i-dependent and -independent mechanisms may account for quartz-induced ROM production in PMNL.