Screening of synthetic peptides derived from the second intracellular (i2) loops of S1P₁ and S1P₃. (A) Sequences of i2 loop–derived peptides and their activities in aortic ring assay. (B) Penetration into the cell. HUVECs were incubated with biotin-tagged KRX-725 for 10 and 30 minutes. Nonbiotinilated KRX-725 was used as control. Fixed and permeabilized cells were reacted with FITC-conjugated extravidin. Visualization was done using confocal microscope (axiovert M135; Zeiss). Micrographs were taken under × 63 objective.