Pretreatment of endothelial cells with RhoK inhibitor diminishes monocyte migration and prevents TEER decrease. (A) TEER was investigated after application of 105 monocytes to the BBB (with or without addition of MCP-1 to the lower chamber). Application of monocytes (0.5 and 1 hours) resulted in a significant decrease of TEER that paralleled the rate of monocyte migration into the lower chamber (B). Pretreatment of endothelial cells in the upper chamber with RhoK inhibitor, Y-27632 (2 hours; 10 μM), attenuated the TEER decrease and diminished monocyte migration across the BBB. TEER results (A) were normalized to measurements in the BBB without monocytes (a value of 100%). Migrated monocytes (immunostained with CD68) were counted in 20 random fields (objective, × 20) in each well. Values represent mean of quadruplicate determinations ± SEM.