Breakdown of F-actin in PC12 cells by NO donors. A. Representative fluorescent images of F-actin in PC12 cells treated with various concentrations of NOR1 or NOR3. PC12 cells (3 × 104 cells/well) were incubated for 5 min with various concentrations of NOR1 or NOR3. Cells were fixed with 4% paraformaldehyde, and labeled with Alexa Fluor 488-phalloidin for F-actin. Bar = 5 μM. B, C. Concentration dependency (B) and time course (C) of F-actin breakdown by NOR1 or NOR3. Fluorescence intensity of more than 40 single cells/dish was quantified by ImageJ as described in "Methods." Data are the mean ± SEM of 3 independent experiments. **P < 0.01 vs. 0 μM NOR1; #P < 0.05; ##P < 0.01 vs. 0 μM NOR3.