title: Sublethal oxidant stress induces a reversible increase in intracellular calcium dependent on NAD(P)H oxidation in rat alveolar macrophages.
abstract: A concentration-dependent elevation of intracellular calcium ([Ca2+]i) and oxidation of NAD(P)H occurred in alveolar macrophages during exposure to sublethal tert-butylhydroperoxide concentrations (tBOOH) (< or = 100 microM in 1 ml with 1 x 10(6) cells). Oxidation of NAD(P)H preceded a rise in [Ca2+]i. The elevation of [Ca2+]i was reversible at < 50 microM tBOOH exposure and the return to the steady state [Ca2+]i correlated temporally with repletion of NAD(P)H. At > 50 microM tBOOH, the changes in NAD(P)H and [Ca2+]i were sustained. The relative contributions of NADPH and NADH oxidation were examined by varying the substrates supplying reducing equivalents and by inhibiting glutathione reductase activity. The results suggested that at < 50 microM tBOOH, oxidation of NADPH predominated, while at > 50 microM tBOOH, NADH oxidation predominated. A complex relationship between the relative roles of NADPH and NADH oxidation and the elevation of [Ca2+]i was revealed: (i) reversible oxidation of NADPH is associated with the initial and reversible elevation of [Ca2+]i at < 50 microM tBOOH; (ii) the sustained elevation of [Ca2+]i at > 50 microM tBOOH correlates with the sustained oxidation of NADH; and (iii) the changes in [Ca2+]i did not depend on influx of extracellular Ca2+. We speculate that at low tBOOH, Ca2+ was released from the NADPH/NADP(+)-sensitive mitochondrial Ca2+ pool while higher tBOOH caused additional Ca2+ release from GSH/GSSG-sensitive nonmitochondrial Ca2+ pools with sustained elevation of [Ca2+]i due to decreased mitochondrial Ca2+ reuptake.
authors.affiliation: Department of Pediatrics, University of Southern California, Childrens Hospital Los Angeles 90027.
authors.forename: F R
authors.initials: FR
authors.lastname: Livingston
authors.forename: E M
authors.initials: EM
authors.lastname: Lui
authors.forename: G A
authors.initials: GA
authors.lastname: Loeb
authors.forename: H J
authors.initials: HJ
authors.lastname: Forman
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents; D066298:In Vitro Techniques; D007211:Indoles; D007700:Kinetics; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism*; D009243:NAD / Q000378:metabolism*; D009249:NADP / Q000378:metabolism*; D016877:Oxidants / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010545:Peroxides / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D020122:tert-Butylhydroperoxide
chemical_list: D002614:Chelating Agents; D007211:Indoles; D016877:Oxidants; D010545:Peroxides; D009243:NAD; C059587:Indo-1 pentaacetoxymethyl ester; D009249:NADP; D020122:tert-Butylhydroperoxide; D002118:Calcium