Modulation of the kinetics of induced neutrophil superoxide generation by fluoride

Fluoride (F-) is unique in that, depending upon concentration, it can either stimulate or inhibit the synthesis of the neutrophil's major intracellular microbicidal product, superoxide anion (O2-). While a number of studies have delved into F- induction of O2- generation, little has been reported on the effect of F- on the synthesis of O2- induced by other agents. In this report, we show that F- inhibits the activation and activity of neutrophils induced either by formyl-methionyl-leucylphenylalanine (FMLP) or by phorbol myristate acetate (PMA). The extent of increase in lag period and decrease in velocity of O2- synthesis was found to be directly related to the concentrations of F- and of hydrogen ion in the medium and to the length of contact time between the neutrophil and F-. Decreasing the pH of the medium, while maintaining a constant concentration of F-, disproportionately increased the inhibitory effect of the anion over the effect of pH alone. Fluoride inhibited the responsiveness of neutrophils to FMLP more than it did their responsiveness to PMA. A gradual but partial reversal of F-'s inhibition of O2- synthesis could be achieved by transferring inhibited cells to F(-)-free medium. Our study shows that the suppression of both FMLP- and PMA-induced synthesis of O2- by neutrophils is most dramatic at a reduced pH and is probably related to the intracellular accumulation of F-.(ABSTRACT TRUNCATED AT 250 WORDS)