title: The inhibition by dantrolene of L-arginine transport and nitric oxide synthase in rat alveolar macrophages.
abstract: 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 microg/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 microM) or inhibitors of NOS, such as aminoguanidine (100 microM), N(G)-monomethyl-L-arginine (100 microM), 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Graduate Institute of Medical Sciences and Department of Medical Research, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan, Republic of China.
authors.forename: T C
authors.initials: TC
authors.lastname: Chou
authors.forename: C Y
authors.initials: CY
authors.lastname: Li
authors.forename: C C
authors.initials: CC
authors.lastname: Wu
authors.forename: M H
authors.initials: MH
authors.lastname: Yen
authors.forename: Y A
authors.initials: YA
authors.lastname: Ding
mesh_terms: D000818:Animals; D001120:Arginine / Q000493:pharmacokinetics*; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D003620:Dantrolene / Q000494:pharmacology*; D007371:Interferon-gamma / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D016676:Macrophages, Alveolar / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D052247:Nitric Oxide Synthase Type II; D051381:Rats; D017207:Rats, Sprague-Dawley; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D008070:Lipopolysaccharides; D019323:omega-N-Methylarginine; D007371:Interferon-gamma; D001120:Arginine; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D003620:Dantrolene; D002118:Calcium