Modulation of the rat alveolar macrophage respiratory burst by hydroperoxides is calcium dependent.
Arch Biochem Biophys 1996;
326:166-71. [PMID:
8579366 DOI:
10.1006/abbi.1996.0061]
[Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Sublethal concentrations of hydroperoxides (H2O2 or tert-butylhydroperoxide) produce a dual effect upon the respiratory burst of rat alveolar macrophages in which low concentrations (< 50 microM) enhance and higher concentrations (> 50 microM) produce inhibition (J. K. Murphy, et al., Free Radical. Biol. Med. 18, 37-45, 1995). These effects correlate with transient versus sustained elevation of [Ca2+]i caused by exposure to hydroperoxides prior to stimulation of the respiratory burst. In the present study changes in [Ca2+]i caused by exposure to sublethal levels of hydroperoxide were buffered by incubating macrophages with the acetoxy-methyl ester of BAPTA, an intracellular Ca2+ chelator. The enhancement of the phorbol ester-stimulated respiratory burst by tBOOH was abolished by BAPTA, while the inhibition was attenuated. Thus, the modulation by tBOOH appears to be largely dependent upon the changes in [Ca2+]i. Receptor mediated stimulation of the respiratory burst (ADP stimulation) involves release of Ca2+ from the inositol-1,4,5-triphosphate (IP3)-sensitive pool in the endoplasmic reticulum. Comparisons were made of the effects of thapsigargin (TG), an endoplasmic reticulum Ca-ATPase inhibitor, with tBOOH on release of intracellular Ca2+ and the respiratory burst. Treatment with TG did not affect changes in [Ca2+]i caused by tBOOH or vice versa. Although TG decreased the ADP-stimulated respiratory burst, it had no effect upon tBOOH modulation. Thus, the effect of tBOOH upon the respiratory burst is dependent upon the release of Ca2+ and the release of Ca2+ occurs from a non-IP3-dependent pool. This aberrant mimicry of normal signal transduction underlies oxidative modulation of the respiratory burst.
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