Cyclosporine A prevented Reactive Oxygen Species (ROS) production and mMTP opening induced by thapsigargin in mutant huntingtin cells. A, representative fluorescence images of 2,7-dichlorofluorescein indicating the levels of ROS striatal cells challenged with 1 μM thapsigargin (Th) for 1 h, CsA for 2 h and both. Increased levels of ROS in striatal cells treated with thapsigargin (A and B) were prevented by pretreatment with CsA. Bar =10 μm. B, Quantitative ROS levels. Data are the mean ± S.E.M. of 3 independent experiments. *, p < 0.05 compared with thapsigargin treated wild type cells; **, p < 0.05 compared with thapsigargin treated wild type cells. ***, p < 0.05 compared with mutant cells treated with thapsigargin. p < 0.05 by non-paired Student’s t test. C and D, representative fluorescence images of wild type (C) and mutant cells (D) cells loaded with calcein AM/Cobalt for 30 min indicating the state of the mPTP . Cells were treated with 1 μM thapsigargin (Th) for 30 1 h and pre-treated with 0.5 μM CsA for 2 h. Treatment with thapsigargin decreased calcein fluorescence intensity in mutant cells indicating that calcium overload opens the mPTP (C). Treatment with CsA prevented the loss of calcein intensity in mutant cells, closing the mPTP. In C and D bar represents 10 μM. E, Calcein intensity levels in striatal cells treated with indicated conditions for 1 h. Quantitation in treated mutant cells revealed that thapsigargin induced mPTP opening. CsA prevented mPTP opening in mutant cells exposed to thapsigargin. Mitochondria depolarization induced by FCCP did not affect mPTP in mutant huntingtin cells. Data correspond to the mean ± S.E.M. of 4 independent experiments. * p < 0.05 compared with wild type cells treated with thapsigargin. ** p < 0.05 compared with mutant cells treated with thapsigargin.