RACK1 depletion attenuates EC barrier function. Non transfected (ctr), non silencing or RACK1 specific silencing RNA transfected HPAEC were plated (5 x 105 cells/well) onto two 8W10E arrays 48 h post-transfection. (A): The initial resistance values at the beginning of the measurement were about 300 Ω and the impedance was measured for 20 hrs after the seeding. (B,C): After overnight incubation and basal TER monitoring (900–1200 Ω), HPAEC monolayers were treated with 50 μM forskolin (B) or 1 μM sphingosine 1-phosphate (S1P) (C). Relative resistances that were detected at the time of maximal TER increase of forskolin/S1P treated cells are shown for each sample. The results are presented as means ± SEM at least of four chambers for each treatment.