Study on action mode of sphingosine 1-phosphate in rat hepatocytes

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 Ca(2+) concentration by S1P. One is through phospholipase C, and the other is through intracellular Ca(2+) channels operated by S1P. The Mn(2+) quenching method was applied to elucidate the action mode of S1P-induced Ca(2+) mobilization in rat hepatocytes. In permeabilized hepatocytes, inositol trisphosphate induced Mn(2+) quenching, and it was blocked by heparin. However, S1P did not induce Mn(2+) quenching. Results suggest that S1P did not mobilize Ca(2+) through intracellular Ca(2+) channels.