Fig. 4. Calcium uptake and release by isolated mitochondria. Extra-mitochondrial free calcium concentration was measured with the calcium probe fluo-5N. (A) Energized mitochondria from A. franciscana lowered the concentration of exogenously added Ca²⁺ at all concentrations investigated compared with controls (no mitochondria present). Calcium-induced calcium release was not observed, consistent with the lack of MPTP opening. (B) Rat liver mitochondria reduced the free Ca²⁺ concentration only in the case where no exogenous Ca²⁺ was added. Upon addition of 0.1 mmol l^–1 Ca²⁺, release of calcium was observed, indicating MPTP opening. For further explanation, refer to text. Each bar represents the mean ± s.d. of N=3 experiments. ^*Significantly different from control (P<0.05) (modified from Menze et al., 2005b).