Inhibition of neutrophil superoxide secretion by of preservative, methylhydroxybenzoate: Effects mediated by perturbation of intracellular ca²⁺?

The preservative, methylhydroxybenzoate inhibited O₂^- secretion from human neutrophils activated by both the chemotactic peptide fMet-Leu-Phe and phorbol myristate acetate (PMA): the low level of oxidant secretion activated by the ionophore A23187 was similarly reduced in preservative-treated suspensions. Oxidant secretion was similarly reduced in fMet-Leu-Phe and A23187 treated suspensions in which intracellular Ca²⁺ was buffered by loading with Quin-2, indicating that methylhydroxybenzoate may exert its effects by perturbation of intracellular Ca²⁺ -dependent processes. Methylhydroxybenzoate could mimic EGTA in preventing the Ca²⁺ dependent enhancement of trypsin activity and could also bind this cation in experiments using a Ca²⁺ electrode, although the preservative bound Ca²⁺ more slowly and had a lower affinity than EGTA. These data indicate that methylhydroxybenzoate may exert its effects on neutrophils by perturbation of Ca²⁺-dependent activation pathways and this phenomenon may also explain its other known pharmacological effects. Furthermore, these observations provide an insight into the mechanisms by which intracellular Ca²⁺ may regulate oxidant secretion.