Nanomolar arachidonic acid influences the respiratory burst in eosinophils and neutrophils induced by GTP‐binding protein: A comparative study of the respiratory burst in bovine eosinophils and neutrophils

Abstract

To investigate a possible role of phospholipase A2 (PLA2) in the respiratory burst in bovine eosinophilic and neutrophilic leukocytes dependent on GTP‐binding protein (G‐protein), we permeabilized these cells with Staphylococcus aureusα‐toxin and induced NADPH oxidase activity with the non‐hydrolysable GTP analogue GTP[S] or the aluminium tetrafluoro complex AlF4−. Under same experimental conditions, cells responded with different onset times. The onset time for eosinophils was 50–200 s, for neutrophils it was only a few seconds. GTP[S] stimulated in neutrophils only 5% of the respiratory burst compared to eosinophils, whereas AlF4−‐induced comparable responses (neutrophils 120% of eosinophils). GDP inhibited these responses with an IC50 value of 2.4 mM. Arachidonic acid showed, with the exception of AlF4− stimulated neutrophils, on both stimuli and cell types an enhancing effect (150%) that reached its maximum at 0.1–1 μM. The PLA2 inhibitor 4‐bromophenacylbromide reduced the GTP[S]‐ and AlF4−‐induced response almost completely (10 μM) and the inhibition was not significantly different for eosinophils and neutrophils (IC50 1–3 μM). If the respiratory burst was reduced with 4‐bromophenacylbromide to 1–4% of the original value, 10% of the basal NADPH oxidase activity could be restored by addition of only 20–100 nM arachidonic acid. In addition, the PLA2 activator adriamycin enhanced the response in a dose‐dependent manner and in the same order as arachidonic acid did. The results presented above suggest that the respiratory burst may be regulated by different low‐molecular‐mass and/or heterotrimeric G‐proteins and an active role for arachidonic acid or its metabolites in the activation and the maintenance of the direct G‐protein‐stimulated respiratory burst in bovine eosinophils and neutrophils. Copyright © 1993, Wiley Blackwell. All rights reserved