Possible Involvement of Cell Surface Receptors in Sphingosine 1-Phosphate-Induced Activation of Extracellular Signal-Regulated Kinase in C6 Glioma CellsSato, Koichi; Tomura, Hideaki; Igarashi, Yasuyuki; Ui, Michio; Okajima, Fumikazu · Molecular Pharmacology · 1999