Fig. 7. PDE4D4 activity is necessary to maintain PMVEC barrier integrity in the presence of increased cAMP synthesis. Direct stimulation of adenylyl cyclase using 1 µM forskolin does not alter cell-cell interaction in confluent control PMVEC monolayers (top row) or in cells expressing the GFP vector (bottom row). However, forskolin induces gap formation in PMVECs expressing the catalytically inactive PDE4D4-GFP fusion peptide (second row). Regions of the images in the second panel (white boxes) were expanded to highlight areas of gap formation (third row). Arrows indicate initial gap formation. Time-lapse videos corresponding to these images are included as Movies 1-3 in supplementary material.