Glucose- and phorbol myristate acetate-stimulated oxygen consumption and superoxide production in rat peritoneal macrophages is inhibited by dexamethasone.
1. Rat peritoneal macrophages stimulated with phorbol 12-myristate 13-acetate (PMA) (40 nM) show an increase in the rate of oxygen consumption (measured with an O2 electrode) and the production of superoxide (measured by cytochrome c reduction), which are both dependent on the presence of exogenous glucose. There is a 1:1 correlation between the oxygen consumed and the superoxide produced over a range of glucose concentrations (0-10 mM). 2. Preincubation of macrophages with dexamethasone (1 microM) for 3 h significantly decreased the Vmax. for PMA-induced glucose-dependent oxygen consumption (P < 0.001) and glucose-dependent superoxide production (P < 0.001). However, dexamethasone did not significantly change the Km for glucose in either PMA-induced oxygen consumption or superoxide production. Dexamethasone is therefore a non-competitive inhibitor of PMA-stimulated glucose-dependent oxygen consumption (Ki = 0.83 +/- 0.09 microM) and superoxide generation (Ki = 0.87 +/- 0.09 microM). 3. The PMA-induced rate of oxygen consumption by macrophages was decreased at oxygen concentrations below approx. 15 microM. The Km of oxygen for PMA-induced oxygen consumption was 1.28 +/- 0.13 microM (n = 12), and this was not significantly different in the presence of dexamethasone; Km = 1.61 +/- 0.31 microM (n = 12). It is therefore concluded that in vivo macrophage superoxide production is not limited by external oxygen or glucose concentrations, even in hypoxic joints.
Biomedical Sciences Division, Kings College London, U.K.
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D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology*; D005947:Glucose / Q000494:pharmacology*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects*; D010529:Peritoneal Cavity / Q000166:cytology; D051381:Rats; D017208:Rats, Wistar; D013481:Superoxides / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D013481:Superoxides; D003907:Dexamethasone; D005947:Glucose; D013755:Tetradecanoylphorbol Acetate