ALA-PDT induced cell death is mediated through the activation of AMP-activated protein kinase. (A) Western blot analysis of phosphorylated AMPK (p-AMPK) expression in PC12 and CL1-0 cells treated with ALA-PDT under the light dose of 2 and 12 J/cm2, respectively. Equal amounts of protein (50 μg) from ALA-PDT-treated cells were loaded at each lane as confirmed by β-actin level. (B) Involvement of AMPK in the ALA-PDT mediated cell death. PC12 (left panel) and CL1-0 (right panel) cells were incubated with 1 mM ALA for 3 hr in the presence of different concentration of Compound C (AMPK inhibitor) for 30 min before light irradiation. Cellular cytotoxicity was determined using Trypan Blue exclusion assay. Values are expressed as a percentage relative to those obtained with cells without Compound C treatment. The figure is a representative of three independent experiments and the results are shown as mean ± SD. Significantly different from ALA only; *P < 0.05, **P < 0.01.