Fig. 2.   Effect of retinoic acids on MPT activity in heart mitochondria. Heart mitochondria were incubated at 1 mg of protein/ml, as described under Materials and Methods. Mitochondria were energized with 10 mM succinate. Rhodamine 123 was added 2 min before adding MPT inducers. A, effects of 9cisRA (b), 13cisRA (c), and atRA (d) at 30 µM. a, no additions; e, atRA + 2 µM CsA. B, samples were incubated with increasing concentrations of atRA. a, no additions; b, 10 µM atRA; c, 20 µM atRA; d, 30 µM atRA. C, comparison between the effect of atRA and Ca²⁺ individually and in combination. a, 0.5 µM Ca²⁺; b, 10 µM atRA; c, 0.5 µM Ca²⁺ + 10 µM atRA. D, samples were incubated with atRA at 30 µM and with increasing concentrations of EGTA. a, atRA; b, atRA + 30 µM EGTA; c, atRA + 100 µM EGTA. The data shown here are representative of two independent experiments with similar results.