Dynamic changes in neutrophil cytoskeleton during priming and subsequent surface stimulated functions

The naturally occurring inositol polyphosphate, inositol hexakisphosphate (InsP6, phytic acid) primes human neutrophils for enhanced responses to stimulatory agonists. Unlike other primers InsP6 has no effect at high doses (up to 500 microM) on the neutrophil's basal rate of superoxide production (O2-). Pretreatment of the cells for 2 min with InsP6 (100 microM) substantially enhances fMet-Leu-Phe (FMLP) (10(-7) M)-induced respiratory burst. In investigations of the dynamic aspect of neutrophil actin during priming and stimulation with FMLP the content of F-actin has been measured with and NBD (nitrobenz-2-oxa-1,3-diazole)-phallacidin assay. The induced assembly of F-actin is rapid (peaks at approximately 45 s) followed by depolymerization. In contrast, priming with InsP6, with or without FMLP stimulation, results in a sustained assembly of F-actin as visualized with a rhodamine-phalloidin staining technique. These changes in macromolecular status and distribution of F-actin during InsP6 priming occur in the absence of any other demonstrable functional responses and thus InsP6 may be a useful tool to follow early events in neutrophil functions or to monitor the presence of unprimed and preprimed subpopulations in the circulation. Since InsP6 is present in high concentrations in neutrophils (up to 100 microM), its release from damaged or effete cells may have a modulatory role on neutrophil functions.