title: Role of sphingosine-1-phosphate inβ-adrenoceptor desensitization via Ca(2+) sensitization in airway smooth muscle.
abstract: BACKGROUND
  The correlation between inflammatory cells and airway smooth muscle plays fundamental roles in the pathophysiology of asthma. This study was designed to determine whether pre-exposure of airway smooth muscle to sphingosine-1-phosphate (S1P), which is released from mast cells by allergic reactions, causes a deterioration of β-adrenoceptor function.
  
  
  METHODS
  Isometric tension and the ratio of fluorescence intensities at 340 and 380 nm (F(340)/F(380)), an indicator of intracellular Ca2+ levels, were simultaneously measured using fura-2 loaded guinea-pig tracheal tissues. Intracellular cAMP levels were also measured.
  
  
  RESULTS
  Pre-exposure to S1P caused a reduction in the inhibitory effects of 0.3μM isoprenaline, a β-adrenoceptor agonist, and 10μM forskolin, a direct activator of adenylyl cyclase, against 1μM methacholine-induced contraction in concentration- and time- dependent manners. In contrast, the values of F(340)/F(380) were not augmented under this experimental condition. After incubation with S1P in the presence of 0.001-1μM Y-27632, a Rho-kinase inhibitor, the reduced responsiveness to forskolin induced by S1P was reversed in a concentration-dependent manner. Moreover, pre-treatment with pertussis toxin (PTX), an inhibitor of G(i), suppressed the loss of forskolin-induced relaxation induced by S1P. Pre-exposure to S1P markedly inhibited the augmentation of cAMP accumulation induced by forskolin. However, addition of Y-27632 and pre-exposure to PTX returned forsokin-induced cAMP accumulation to the control level.
  
  
  CONCLUSIONS
  Pre-exposure to S1P causes heterologus desensitization of β-adrenoceptors by increasing the sensitivity of airway smooth muscle to intracellular Ca2+. Ca2+ sensitization regulated by G(i) and Rho-kinase is involved in this phenomenon.
authors.affiliation: Department of Respiratory Medicine, Nagoya University Graduate School of Medicine, Aichi, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Makino
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kume
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Oguma
authors.forename: Mihoko
authors.initials: M
authors.lastname: Sugishita
authors.forename: Akira
authors.initials: A
authors.lastname: Shiraki
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Hasegawa
authors.forename: Haruo
authors.initials: H
authors.lastname: Honjo
authors.forename: Kaichiro
authors.initials: K
authors.lastname: Kamiya
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000577:Amides / Q000494:pharmacology; D000818:Animals; D001249:Asthma / Q000188:drug therapy / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D006168:Guinea Pigs; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D008246:Lysophospholipids / Q000494:pharmacology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D037342:Pertussis Toxin / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014132:Trachea / Q000473:pathology; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors
chemical_list: D000318:Adrenergic beta-Agonists; D000577:Amides; D008246:Lysophospholipids; D011725:Pyridines; D011943:Receptors, Adrenergic, beta; C108830:Y 27632; C060506:sphingosine 1-phosphate; D037342:Pertussis Toxin; D054460:rho-Associated Kinases; D007545:Isoproterenol; D013110:Sphingosine