Modulation of the alveolar macrophage respiratory burst by hydroperoxides

Exposure of alveolar macrophages to hydroperoxides (ROOH) inhibits subsequent stimulation of O2·− production (the respiratory burst). Previous studies (under nonoxidant stress conditions) have shown that elevation of intracellular free calcium ([Ca2+]i) participates in both initiation and termination of O2·− production. In this investigation, the effects of sublethal ROOH exposure on [Ca2+]i and the respiratory burst of rat alveolar macrophages were compared. Exposure to a sublethal range of H2O2 or tert-butylhydroperoxide (10–100 pmol/106 cells; initially 10–100μM under the experimental conditions) for 15 min resulted in dose-dependent effects on the respiratory burst stimulated by various agents, ADP, ATP, zymosan-activated serum, and phorbol myristate acetate. Low concentrations of the ROOH (10 or 25 pmol/106 cells) were found to enhance stimulation, whereas exposure to 75 or 100 pmol/106 cells resulted in significant inhibition for all of the stimuli. All concentrations of ROOH caused a rapid elevation in [Ca2+]i. For those concentrations of ROOH that produced enhancement of subsequent stimulation of the respiratory burst, [Ca2+]i returned to near baseline before the end of the 15-min preincubation. The temporal- and concentration-dependent effects of ROOH on [Ca2+]i correlate with subsequent enhancement or inhibition of stimulated O1·− production. Similarities between the ROOH-induced changes in [Ca2+]i and the effect of [Ca2+]i changes in physiological regulation of the respiratory burst suggest a potential relationship.