Effects of inhibiting Rac1 or myosin II on stress fiber and focal adhesion densities in cells migrating inside 6-µm channels. CHO-α4WT, CHO-α4Y991A, and CHO-α4Y988A cells were induced to migrate inside 6-µm VCAM-1–coated channels in the presence of vehicle control (a–c), NSC23766 (d–f), or blebbistatin (g–-i). Cells were stained with TRITC-conjugated phalloidin and imaged by confocal microscopy. The boxes at the bottom left corner of each image show an enlarged view highlighting the stress fibers. The dotted lines indicate the PDMS walls of the channel.