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The Inhibition by Dantrolene of L-Arginine Transport and Nitric Oxide Synthase in Rat Alveolar Macrophages

Dantrolene decreases the free cytosolic Ca2+ level via inhibition of calcium release from the sacroplasmic reticulum.However, the effect of dantrolene on L-arginine transport and nitric oxide synthase (NOS) activity is still unknown. In this study, we examined the effects of dantrolene on L-arginine transport and activity of inducible nitric oxide synthase (iNOS) induced by lipopolysaccharide (LPS) and interferon gamma (IFN-gamma) in rat alveolar macrophages. Incubation of cells with LPS (1 [micro sign]g/mL) and IFN-gamma (100 u/mL) for 24 h resulted in significant increases in nitrite production and L-arginine transport. In the presence of dantrolene (100 [micro sign]M) or inhibitors of NOS, such as aminoguanidine (100 [micro sign]M), NG-monomethyl-L-arginine (100 [micro sign]M), the nitrite production and L-arginine transport were significantly inhibited compared with that in the LPS + IFN-gamma group. Furthermore, the results of kinetic analysis indicate that the suppression of L-arginine transport by dantrolene was caused by selective decrease of the velocity of transport (Vmax) without affecting the affinity (Km) for L-arginine. In addition, dantrolene also attenuated the activity of iNOS in a dose-dependent manner. We conclude that the mechanisms by which dantrolene attenuated NO synthesis may be associated with the inhibition of availability of L-arginine by reducing the affinity for L-arginine, accompanied by a parallel decrease of the activity of iNOS. Implications: In this study, we demonstrated that dantrolene, a drug that reduces the intracellular Ca2+ level, can inhibit L-arginine availability and inducible nitric oxide synthase activity in macrophages. Our finding may provide a novel therapeutic approach using dantrolene to prevent hypotension associated with an activation of inducible nitric oxide synthase in endotoxemia. (Anesth Analg 1998;86:1065-9)