Modulation of the rat alveolar macrophage respiratory burst by hydroperoxides is calcium dependent.
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.
Hoyal
C R
CR
Department of Molecular Pharmacology and Toxicology, University of Southern California, Los Angeles 90033, USA.
Gozal
E
E
Zhou
H
H
Foldenauer
K
K
Forman
H J
HJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology*; D016676:Macrophages, Alveolar / Q000378:metabolism*; D008297:Male; D016877:Oxidants / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016897:Respiratory Burst / Q000187:drug effects*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D004791:Enzyme Inhibitors; D016877:Oxidants; D013729:Terpenes; D019284:Thapsigargin; D006861:Hydrogen Peroxide; D002118:Calcium