Treatment with Cyclosporine A improved mitochondrial calcium uptake in mutant huntingtin cells exposed to calcium overload. A, striatal cells were loaded with Rhod2 AM dye to determine mitochondrial calcium levels in cells exposed to 1 μM thapsigargin (Th) during 30 min. Thapsigargin treatment severely decreased mitochondrial calcium uptake. Striatal cells were incubated for 2 h with 0.5 μM Cyclosporine A (CsA) prior to determination of mitochondrial calcium levels in response to thapsigargin treatment. CsA prevented the mitochondrial calcium decrease induced by thapsigargin in the mutant cells. B, quantification of mitochondrial calcium levels from 4 independent experiments obtained from cells exposed to thapsigargin for 30 min. *, p < 0.05 compared with mutant cells treated with thapsigargin alone. C, wild type and mutant cells were pre-treated with 1 μM ruthenium red for 1 h, before addition of 1 μM thapsigargin. Ruthenium red did not prevent the mitochondrial calcium decrease induced by thapsigargin in mutant cells. D, quantification of mitochondrial calcium uptake at 30 min shows that thapsigargin only induced a significant increase in mitochondrial calcium only in wild type cells. Thapsigargin treatment of mutant cells resulted in a pronounced decrease in mitochondrial calcium uptake by mutant cells, and this event was partially blocked by CsA pre-treatment. Data are the mean ± S.E.M. of 3 separate experiments. *, p < 0.05 compared with mutant cells treated with thapsigargin; **, p < 0.05 compared with mutant cells treated with thapsigargin plus CsA. p < 0.05 for nonpaired Student’s t test.