Phloretin is a potent inhibitor of rabbit neutrophil activation by chemotactic factors.

We have studied the effect of phloretin, a compound known to interfere with carrier mediated transport processes, on the functional responsiveness of rabbit neutrophils. Phloretin was found to inhibit neutrophil degranulation, aggregation and calcium uptake stimulated by the chemotactic peptide fMet-Leu-Phe. Part of these effects of phloretin may be accounted for by its interference with the binding of the synthetic peptide to its plasma membrane receptors. However, phloretin also inhibits the arachidonic acid and leukotriene B4 induced calcium uptake. These results imply that phloretin affects a component of membrane structure which is central to the activation sequences available to the neutrophils. The results of the present experiments demonstrate that phloretin can interfere with stimulus-response coupling in soluble mediator ('hormone') responsive cells.