Fig. 1. Pretreatment with low concentrations of valproate increases resistance to ER stress-induced cell death. (A) HepG2 cells were cultured in the presence of various concentrations of valproate as indicated. Lactate dehydrogenase (LDH) activity was determined in media after 48 hours. The plot represents LDH released after exposure to valproate as a percentage of the total LDH activity recovered from control cells lysed with 0.5% Triton X-100. Data are presented as the mean±s.d. of three separate experiments. (B) LDH release assay measuring cell death in HepG2 cells pretreated with 0 mM () or 0.5 mM () valproate for 18 hours and then exposed for 6 hours to the calcium ionophore, A23187 (0-10 µM), tunicamycin (0-40 µg/ml) or H₂O₂ (0-0.5%) as indicated. Results are expressed as the percentage of the total LDH present in untreated cells and depicted as mean±s.d. from three separate experiments. *P<0.01 when compared to levels in the corresponding controls. (C) Determination of caspase 3 activation in HepG2 cells pretreated for 18 hours in the absence or presence of 0.5 mM valproate and then exposed to 0 or 20 mg/ml tunicamycin for 6 hours as indicated. Hatched bars represent cells that were treated with the caspase 3 inhibitor, Z-VAD, in addition to tunicamycin. Caspase 3 activity was determined in the cell lysates and normalized to total protein concentrations. Data are presented as the mean±s.d. of three separate experiments. *P<0.01 when compared to the activity in the corresponding control.