Experiments were designed to investigate whether leukotriene (LTB4) receptors can couple directly to phospholipase A2 (PLA2) in guinea pig eosinophils and the role of endogenous arachidonic acid (AA) in LTB4- induced activation of the NADPH oxidase. LTB4 (EC50 ~ 16 nM) and AA (EC50 ~ 6 μM) generated hydrogen peroxide (H2O2) in a concentration- dependent manner and at an equivalent maximum rate (5-6 nmol/min/106 cells). LTB4 stimulated PLA2 over a similar concentration range that activated the NADPH oxidase, although kinetic studies revealed that the release of [3H]AA (t 1/4 ~ 2 s) preceded H2O2 generation (t 1/4 > 30 s). Pretreatment of eosinophils with pertussis toxin abolished the increase in inositol(1,4,5)trisphosphate mass, [Ca2+](c), [3H]AA release, and H2O2 generation evoked by LTB4. Qualitatively identical results were obtained in eosinophils in which phospholipase C (PLC) was desensitized by 4β-phorbol 12,13-dibutyrate with the exception that [3H]AA release was largely unaffected. Additional studies performed with the protein kinase C inhibitor, Ro 31-8220, and under conditions in which Ca2+ mobilization was abolished, provided further evidence that LTB4 released [3H]AA independently of signal molecules derived from the hydrolysis ofphosphatidylinositol(4,5)bisphosphate by PLC. Pretreatment of eosinophils with the PLA2 inhibitor, mepacrine, abolished LTB4-induced [3H]AA release at a concentration that inhibited H2O2 by only 36%. Collectively, the results of this study indicate that agonism of LTB4 receptors on guinea pig eosinophils mobilizes AA by a mechanism that does not involve the activation of PLC. In addition, although LTB4 effectively stimulated PLA2, a central role for AA in the activation of the NADPH oxidase was excluded.
|Number of pages||9|
|Journal||Journal of Immunology|
|Publication status||Published - 1 May 1998|
ASJC Scopus subject areas
- Immunology and Allergy