LTB₄ release by human lung macrophages via receptor not voltage operated Ca²⁺ channels

¹ Airways Disease, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, London, SW3 6LY, UK
² Novartis Institutes for BioMedical Research, Wimblehurst Road, Horsham, West Sussex, RH12 5AB, UK
³ Histopathology, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, London, SW3 6LY, UK
⁴ Chest Clinic, King Edward King VII Hospital, St. Leonard's Road, Windsor, Berkshire, SL4 3DP, UK

^* To whom correspondence should be addressed. E-mail: l.donnelly{at}imperial.ac.uk.

	Abstract

Increased numbers of macrophages and neutrophils in the lung is a key feature of chronic obstructive pulmonary disease (COPD). The major neutrophil chemotactic agent in the airways of COPD patients is leukotriene (LT)B₄ and is released by macrophages. This study examined the role and mechanism of Ca²⁺ in PAF-stimulated LTB₄ release from human lung macrophages.

Macrophages were isolated from lung tissue from subjects undergoing lung resection surgery and monocyte-derived macrophages (MDM) were obtained from non-smokers, smokers without obstruction and COPD patients. Cells were stimulated with PAF and LTB₄ release and [Ca²⁺]_i measured.

Lung macrophages and MDM released LTB₄ following stimulation with PAF (EC₅₀: 0.08±0.06 µM, n=5 vs. 0.17±0.12 µM, n=17, respectively). Lung macrophages released 8-fold more LTB₄ compared with MDM. Neither smoking nor COPD altered MDM responses. PAF-stimulated LTB₄ release was abrogated by EGTA suggesting a role for extracellular Ca²⁺. This was substantiated by using store operated channel blockers econazole, SK&F96365 and Gd³⁺. However, econazole and SK&F96365 were more effective in MDM than lung macrophages. Neither LOE908 nor nifedipine could attenuate this response.

These data suggest that PAF-stimulated LTB₄ release from human lung macrophages is mediated, in part, by Ca²⁺ influx through receptor but not voltage-operated Ca²⁺ channels.