Constitutively active RhoA antagonizes effect of alendronate (50 µM) and GGTI-2166 (10 µM), but not Y-27632 (10 µM) on actin stress fibers in MC3T3-E1 cells. After transfection, cells were treated for 6 hr with alendronate, GGTI-2166, or and Y-27632 in BSA media. A: Confocal micrographs of cells showing actin stress fibers. Bars represent 25 µm. B–D: Quantification of parameters. Values are means +/− SEM of responses measured in 2 independent experiments in which 40 cells were imaged and quantified per group. Different letters indicate statistically significant differences (95% Tukey confidence interval) from control (a) and between groups (b). There are no statistically significant differences in edge actin bundle, cellular area, or circularity (data not shown).