Height corresponds to fluorescence intensity of each pixel from confocal images of cells. a, An unstimulated cell. b, A cell stimulated with PtdlnsP3–histone for 30 s. c, A cell stimulated with PtdlnsP3–histone for 150 s. d, A cell expressing the chemokine receptor C5AR–GFP14 stimulated with 100 nM FMLP for 150 s. a′–d′, Confocal images from which the surface plots in a–d were generated.