Role of sphingosine-1-phosphate (S1P) and the S1P2 receptor in allergen-induced, mast cell-dependent contraction of rat lung parenchymal strips

Lung parenchymal strips isolated from ovalbumin-sensitized rats manifest a mast cell-dependent, biphasic contraction when challenged with allergen. The first phase is mediated by the release of preformed 5-HT while the second phase is dependent on de novo synthesis of leukotrienes. Sphingosine 1-phosphate (S1P) is a sphingolipid metabolite which is readily generated in mast cells and has been demonstrated to be an important regulator of allergen-induced mast cell activation. We have used the parenchymal strip to explore the role of sphingosine 1-phosphate and the S1P₂ receptor in the two components of the acute response to allergen. Lung parenchymal strips were prepared from Brown Norway rats actively sensitized to ovalbumin. The strips were set up in organ baths and contractile responses measured isometrically. The inhibitors of sphingosine kinase, D-erythro-NN-dimethylsphingosine (dimethylsphingosine) and 4-[4-(4-chloro-phenyl)-thiazol-2-ylamino]-phenol (SKI-II) inhibited concentration-dependently both phases of the contractile response induced by 0.1 µg ml^?1 ovalbumin. The effects were seen at concentrations similar to those which inhibit the purified enzyme and were selective in that neither the contractile response to adenosine nor that to 5-hydroxytryptamine was affected. JTE-013 (a selective S1P₂ receptor antagonist) also blocked the response to ovalbumin (0.1 µg ml^?1). However, the concentrations of JTE-013 required (µM) were substantially higher than its affinity for the S1P₂ receptors (nM). However, when tested against a lower concentration of ovalbumin (0.03 µg ml^?1), JTE-013 inhibited the response with nM potency. These data demonstrate the importance of S1P and the S1P₂ receptor as regulators of allergen-induced activation of mast cells in their natural environment in the rat lung.