Polymyxin B inhibits phorbol 12-myristate 13-acetate, but not chemotactic factor, induced effects in rabbit neutrophils.

The addition of the amphipathic polycationic antibiotic polymyxin B to a suspension of rabbit neutrophils results in inhibiton of the agonist (secretion of secondary granules) and antagonist (inhibition of chemotactic factor induced degranulation) properties of phorbol 12-myristate 13-acetate. On the other hand, polymyxin B does not inhibit the degranulation of the neutrophils that is induced by chemotactic factors. These results imply that the role of protein kinase C in the initiation of neutrophil functions in response to the addition of chemotactic factors is less critical than previously thought. In addition, the reversal of the inhibitory properties of phorbol esters by polymyxin B indicates that the former are mediated by the ability of the tumor promoters to activate protein kinase C. These results thus strengthen the hypothesis that protein kinase C plays important roles in the regulation (as contrasted to initiation) of neutrophil functions.