The role of carbon monoxide in lucigenin-dependent chemiluminescence of rat alveolar macrophages

We have investigated the role of carbon monoxide (CO) in lucigenin-dependent chemiluminescence of alveolar macrophages from rat lungs. CO (10 nM to 1 μM) decreased chemiluminescence of alveolar macrophages in a concentration-dependent fashion. At a concentration of 1 μM, Co significantly increased intracellular cyclic GMP levels from a control value of 175 ± 25 fmol/2 × 10⁶ cells to 431 ± 49 fmol/2 × 10⁶ cells. Pretreatment of alveolar macrophages with N^G-monomethyl-L- arginine (100 μM) failed to inhibit CO (1 μM)-induced decreases in chemiluminescence of alveolar macrophages (3.7 ± 0.7 cpm × 10³ in the presence of N^G-monomethyl-L-arginine and 3.4 ± 0.6 cpm × 10³ in the absence of N^G-monomethyl-L-arginine) and CO (1 μM)-induced increases in intracellular cyclic GMP levels (452 ± 65 fmol/2 × 10⁶ cells in the presence of N^G-monomethyl-L-arginine and 419 ± 58 fmol/2 × 10⁶ cells in the absence of N^G-monomethyl-L-arginine). Decreases in chemiluminescence of alveolar macrophages induced by CO (1 μM) were concentration-dependently inhibited by methylene blue (from 0.1 μM to 10 μM). Dibutyryl cyclic GMP (db cyclic GMP) (1 mM) also reduced chemiluminescence of alveolar macrophages (1.5 ± 0.3 cpm × 10³ in the presence of db cyclic GMP and 3.6 ± 0.6 cpm × 10³ in the absence of db cyclic GMP). In contrast to CO and db cyclic GMP, zinc protoporphyrin-9 (10 nM to 1 μM), an inhibitor of heme oxygenase potentiated chemiluminescence of alveolar macrophages in a concentration-dependent fashion. Northern blot analysis revealed that alveolar macrophages expressed mRNA of heme oxygenase-1. These results suggest that an endogenous CO-like factor inhibits chemiluminescence of alveolar macrophages via activating guanylate cyclase.