The RhoA inhibitor, C3 exoenzyme, abolishes arecoline-induced actin stress fiber formation. (A) HA22T/VGH cells were left untreated (C), treated with 1.5 μg/ml of C3 exoenzyme for 25 h (Ri1.5), with 100 μg/ml of arecoline for 24 h (A100), or with C3 exoenzyme for 1 h, then with 100 μg/ml of arecoline in the continued presence of C3 exoenzyme for 24 h (Ri1.5+A100), then were fixed with paraformaldehyde for actin labeling and observation of stress fiber by fluorescence microscopy (A) or flow cytometry (B). In B, the values are the percentage of actin staining-cells and are the mean ± S.D. for three independent experiments. The green filled area is the untreated control and those delimited by the black lines the treated groups. *: p < 0.05 as compared to the untreated control; #: p < 0.05 as compared to the arecoline (A100) treatment.