Mechanism of primary Cd2+-induced rat liver mitochondria dysfunction: discrete modes of Cd2+ action on calcium and thiol-dependent domains

We attempted to discern discrete sites of Cd²⁺ deleterious action on rat liver mitochondrial function. In particular, EGTA, ADP, and cyclosporin A (potent mitochondrial permeability transition antagonists) affected mainly Cd²⁺ -induced changes in resting state respiration, eliminating its stimulation in KCl medium, while dithiothreitol (DTT, a dithiol reductant) produced its effect both on Cd²⁺ activation of the basal respiration and Cd²⁺ depression of uncoupler-stimulated respiration, evoking its restoration. Substantial differences in DTT influence on mitochondrial respiration at low and high Cd²⁺] were revealed, namely, an enhanced mitochondrial permeabilization in the presence of saturated DTT] at high Cd²⁺] took place. Besides, DTT only partially reversed Cd²⁺ -induced swelling in NH₄NO₃ medium when glutamate plus malate or succinate without rotenone was used. Contrarily, DTT produced complete reversal of the swelling of succinate-energized mitochondria when rotenone was present in the medium. In addition, in the presence of rotenone both Cd²⁺ -produced activation of the resting state respiration in KCl medium and Cd²⁺-induced swelling in sucrose medium of succinate-energized mitochondria were more sensitive to cyclosporin A than the same Cd²⁺ effects obtained on mitochondria oxidizing succinate (without rotenone) or glutamate plus malate. We have concluded that Cd²⁺, producing primary mitochondrial dysfunction, acts both as a thiol and Me²⁺ binding site reagent. Suppositions about possible localization of separate sites of direct Cd²⁺ effects on mitochondrial function were made.