Figure. Concentration-dependent activation of S1PR1 by S1P. Reporter cells were transfected with either the expression plasmid for sphin­go­sine-1-phos­phate receptor 1 (S1PR1) or the mock plasmid and treated with various concentrations of sphin­go­sine 1-phos­phate (S1P). Data points shown are the mean ± SEM of an experiment performed in triplicate, and the curve is a fit to Hill equation with an EC50 of 7.5 nM.