Constitutive nitric oxide production by rat alveolar macrophages

Abstract

Results from previous studies suggest that alveolar macrophages must be exposed to inflammatory stimuli to produce nitric oxide (⋅ NO). In this study, we report that naive unstimulated rat alveolar macrophages do produce ⋅ NO and attempt to characterize this process. Western blot analysis demonstrates that the enzyme responsible is an endothelial nitric oxide synthase (eNOS). No brain or inducible NOS can be detected. The rate of ⋅ NO production is ∼0.07 nmol ⋅ 106cells−1 ⋅ h−1, an amount that is less than that produced by the eNOS found in alveolar type II or endothelial cells. Alveolar macrophage ⋅ NO formation is increased in the presence of extracellularl-arginine, incubation medium containing magnesium and no calcium, a calcium ionophore (A-23187), or methacholine. ⋅ NO production is inhibited by N G-nitro-l-arginine methyl ester (l-NAME) but not by N G-nitro-l-arginine,l- N 5-(1-iminomethyl)ornithine hydrochloride, or aminoguanidine. Incubation with ATP, ADP, or histamine also inhibits ⋅ NO formation. Some of these properties are similar to and some are different from properties of eNOS in other cell types. Cellular ⋅ NO levels do not appear to be related to ATP or lactate content. Alveolar macrophage production of ⋅ NO can be increased approximately threefold in the presence of lung surfactant or its major component, dipalmitoyl phosphatidylcholine (DPPC). The DPPC-induced increase in ⋅ NO formation is time and concentration dependent, can be completely inhibited by l-NAME, and does not appear to be related to the degradation of DPPC by alveolar macrophages. These results demonstrate that unstimulated alveolar macrophages produce ⋅ NO via an eNOS and that lung surfactant increases ⋅ NO formation. This latter effect may be important in maintaining an anti-inflammatory state in vivo.

A Signaling Pathway Linking Nitric Oxide Production to Heterotrimeric G Protein and Hydrogen Peroxide Regulates Extracellular Calmodulin Induction of Stomatal Closure in Arabidopsis

“…In animal systems, it has been reported that extracellular calcium induces NO production (Miles et al, 1998). In this study, we have checked NO levels after treatment with extracellular calcium, and the results indicated that NO levels in the guard cells of the wild type increased when treated with extracellular calcium (Fig.…”

Tetrahydro-4-Aminobiopterin Attenuates Dendritic Cell-Induced T Cell Priming Independently from Inducible Nitric Oxide Synthase

“…1A). Expression of constitutive NOSs present in addition to iNOS and generating NO in the absence of inflammatory stimuli has been demonstrated in various cell types including rodent macrophages (22)(23)(24). However, in dendritic cells from both wild-type and iNOS Ϫ/Ϫ mice, endothelial nitric oxide synthase as well as neuronal nitric oxide synthase mRNA expression were close to the detection limit of ϳ5 ϫ 10 Ϫ9 mRNA copies per 18 S rRNA (data not shown).…”

Importance of Histamine in the Cytokine Network in the Lung Through H2 and H3 Receptors: Stimulation of IL-10 Production

“…Thus, given our results with L-NAME, it seems that histamine stimulates NO release through a cNOS pathway. Although AMs are well known to produce NO through iNOS, unstimulated AMs can also produce NO via cNOS (45). This may explain why histamine alone stimulated the release of NO, but did not potentiate its release when histamine-pretreated AMs were stimulated with LPS, which increases iNOS.…”