Effects of polymyxin B on superoxide anion release and priming in human polymorphonuclear leukocytes.

We studied the effect of a potent inhibitor of protein kinase C, polymyxin B (PMXB), on superoxide anion (O2-) release by human polymorphonuclear leukocytes (PMNL). PMXB was compared with another inhibitor of protein kinase C, 1-(5-isoquinoline-sulfonyl)-2-methyl piperazine (H-7). Both PMXB and H-7 inhibited phorbol myristate acetate (PMA)-stimulated O2- release. Formyl-methionyl-leucyl-phenylalanine (FMLP)-stimulated O2- release by cytochalasin B-treated PMNL was not inhibited significantly by either PMXB or H-7. 1-Oleoyl-2-acetyl-glycerol (OAG,25-100 microM) stimulated PMNL to release O2- with a long lag-time (8-10 min). Although H-7 inhibited OAG-stimulated O2- release, PMXB augmented the OAG-stimulated response by increasing rate and reducing lag time. The augmenting effect of PMXB was evident only when added after stimulation by OAG, with maximum effect observed at 3 min after addition of OAG. The augmenting effect was also seen with PMXB immobilized on agarose beads. PMXB did not affect the respiratory burst response to 1,2-dioctanoylglycerol. PMXB-augmented, OAG-stimulated O2- release was inhibited by the addition of H-7 before OAG. In contrast to the effect on O2- release, OAG-stimulated protein phosphorylation was inhibited similarly by either PMXB or H-7, when these agents were added 3 min after stimulation by OAG. These results suggested that initial activation of protein kinase C by OAG is essential for O2- release, but that PMXB acts in a manner independent from protein kinase C to augment OAG-stimulated O2- release. When priming by OAG for enhanced O2- release (as opposed to direct stimulation of O2- release) in FMLP-stimulated PMNL was examined, PMXB inhibited O2- release in OAG-primed PMNL, suggesting that protein kinase C is involved in priming of PMNL by OAG.