Characterization of formylmethionyl-leucyl-phenylalanine stimulation of inositol trisphosphate accumulation in rabbit neutrophils

Inositol trisphosphate (IP₃) formed by phospholipase C-mediated breakdown of triphosphoinositide (PIP₂) may be a ubiquitous second messenger for a number of Ca²⁺-mobilizing receptor agonists. Using [³H]inositol-labeled rabbit peritoneal neutrophils, we report that radiolabeled inositol phosphates are generated in response to the chemotactic peptide, formylmethionyl-leucyl-phenylalanine (fMet-Leu-Phe). fMet-Leu-Phe-stimulated formation of [³H]IP₃ occurs with a rapid time course and a concentration dependence which closely parallels that of stimulated lysosomal enzyme secretion. The synthetic peptide methionyl-leucyl-phenylalanine, which is unable to promote secretion, failed to elevate [³H]IP₃ accumulation, and the competitive antagonist t-butyloxycarbonyl-Phe-Leu-Phe-Leu-Phe depressed the stimulant action of fMet-Leu-Phe on [³H]IP₃ levels and secretion. The Ca²⁺ ionophore ionomycin, which promotes secretion, was unable to enhance IP₃ levels, confirming that polyphosphoinositide hydrolysis is a specific receptor-mediated event that precedes calcium mobilization during neutrophil activation. The ability of leukotriene B₄ to also promote a rapid accumulation of [³H]IP₃ suggests that there exists in the neutrophil an interaction between phospholipase A₂ and C-mediated events. These findings support the hypothesis that IP₃ may be a pivotal messenger for signal transfer by Ca²⁺-mobilizing receptor agonists.