TY - JOUR T1 - Recombinant Human G Protein-Coupled Lysophosphatidic Acid Receptors Mediate Intracellular Calcium Mobilization JF - Molecular Pharmacology JO - Mol Pharmacol SP - 881 LP - 888 DO - 10.1124/mol.54.5.881 VL - 54 IS - 5 AU - Songzhu An AU - Thieu Bleu AU - Yuhua Zheng AU - Edward J. Goetzl Y1 - 1998/11/01 UR - http://molpharm.aspetjournals.org/content/54/5/881.abstract N2 - Mobilization of intracellular Ca2+ is a critical cellular response to lysophosphatidic acid (LPA) in many cell types. Recent identification of endothelial differentiation gene (Edg) 2 and Edg4 as subtypes of G protein-coupled receptors for LPA allowed examination of the Ca2+ mobilization mediated specifically by each subtype. To reduce endogenous background levels while enhancing recombinant receptor-specific signals, the aequorin luminescence method was used to quantify cytoplasmic Ca2+ levels. In TAg-Jurkat T cells transiently co-transfected with apoaequorin and human Edg2 or Edg4 cDNA, LPA dose-dependently increased light emission triggered by increased Ca2+ bound to aequorin.N-Palmitoyl-l-serine-phosphoric acid andN-palmitoyl-l-tyrosine-phosphoric acid, which had been previously shown to be antagonists for Xenopus laevis LPA receptors, did not antagonize the Ca2+-mobilizing effects of Edg2 and Edg4. Surprisingly, they acted as agonists or partial agonists for Edg2 and Edg4. The Ca2+ mobilization by Edg2 and Edg4 was further characterized in stable transfectants of rat HTC4 hepatoma cells. By using the fura-2 fluorescence method, a difference in the kinetics of Ca2+ flux with Edg2 and Edg4 was observed. With Edg2, but not Edg4, the initial increase in the Ca2+ concentration was followed by a sustained influx of extracellular Ca2+. The coincident production of inositol phosphates and the inhibition of Ca2+ mobilization by the phospholipase C inhibitor U73122 strongly suggested that Edg2 and Edg4 mobilize Ca2+ through inositol trisphosphate generated by phospholipase C activation. Pertussis toxin almost completely blocked LPA-induced Ca2+mobilization by Edg2 but only partially blocked that by Edg4, which suggests that Edg2 transduces Ca2+ mobilization largely through pertussis toxin-sensitive Gi proteins, whereas Edg4 requires both Gi and Gq. ER -