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Sphingosine-1-phosphate (S1P) acts on a set of G protein-coupled receptors in the plasma membrane and also as a second messenger in certain cell types. There are two possible pathways to mobilize intracellular Ca2+ concentration by S1P. One is through phospholipase C, and the other is through intracellular Ca2+ channels operated by S1P. The Mn2+ quenching method was applied to elucidate the action mode of S1P-induced Ca2+ mobilization in rat hepatocytes. In permeabilized hepatocytes, inositol trisphosphate induced Mn2+ quenching, and it was blocked by heparin. However, S1P did not induce Mn2+ quenching. Results suggest that S1P did not mobilize Ca2+ through intracellular Ca2+ channels. Keywords:: hepatocyte, sphingosine 1-phosphate, second messenger