MODULATION OF THE RAT ALVEOLAR MACROPHAGE RESPIRATORY BURST BY HYDROPEROXIDES IS CALCIUM-DEPENDENT

Sublethal concentrations of hydroperoxides (H2O2 or tert-butylhydroper oxide) produce a dual effect upon the respiratory burst of rat alveola r macrophages in which low concentrations (<50 mu M) enhance and highe r concentrations (>50 mu M) produce inhibition (J. K. Murphy, et al., Free Radical. Biol. Med. 18, 37-45, 1995). These effects correlate wit h transient versus sustained elevation of [Ca2+](i) caused by exposure to hydroperoxides prior to stimulation of the respiratory burst. In t he present study changes in [Ca2+](i) caused by exposure to sublethal levels of hydroperoxide were buffered by incubating macrophages with t he acetoxymethyl ester of BAPTA, an intracellular Ca2+ chelator. The e nhancement 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-tris phosphate (IP3)-sensitive pool in the endoplasmic reticulum. Compariso ns were made of the effects of thapsigargin (TG), an endoplasmic retic ulum Ca-ATPase inhibitor, with tBOOH on release of intracellular Ca2and the respiratory burst. Treatment with TG did not affect changes in [Ca2+](i) caused by tBOOH or vice versa. Although TG decreased the AD P-stimulated respiratory burst, it had no effect upon tBOOH modulation . Thus, the effect of tBOOH upon the respiratory burst is dependent up on the release of Ca2+ and the release of Ca2+ occurs from a non-IP3-d ependent pool. This aberrant mimicry of normal signal transduction und erlies oxidative modulation of the respiratory burst. (C) 1996 Academi c Press, Inc.