Search

Ion permeability of internal membrane and a respiration in isolated rat liver mitochondria, further related to as "sodium ones", were studied following replacement of K+ ions for Na+ ones in the mitochondrial matrix. As compared with the control ("potassium mitochondria"), state 4 respiration in the sodium mitochondria, energized by succinate, was shown to be enhanced in KCl or sucrose media. Oxygen consumption rates in the sodium mitochondria, being in state 3 or stimulated by 2,4-dinitrophenol, were lower than rates for the control mitochondria. This effect was much pronounced in the sucrose medium. The coefficients, characterizing the distribution of 137Cs between mitochondria and the medium, were lower for the sodium mitochondria than for the control in the presence of 2.5 mM succinate and 10(-8) M valinomycin. In comparison with the control, a more extensive swelling for the sodium mitochondria was found, first, in the medium containing 25 mM K-acetate and 100 mM sucrose for succinate-energized mitochondria, and second, in the medium containing 125 mM NH4NO3 without mitochondrial energization. Changes disclosed in respiration, swelling and coefficients of 137Cs distribution for the sodium mitochondria are supposed to be caused by non-uniform effects of Na+ and K+ ions on the water structure of mitochondrial matrix, ion permeability of internal membrane, and the activity in oxidative phosphorylation enzymes.

We studied a change in Cd2+ influence on state 4 and 3 respiration and on 2,4-dinitrophenol (DNP)-stimulated respiration of isolated rat liver mitochondria, after replacement of KCl for equimolar quantities of NaCl, LiCl or for 200 mM sucrose in the incubation medium. Cd2+ concentrations higher than 2.5 microM reduced state 3 respiration or DNP-stimulated one in KCl medium (control), and activated state 4 respiration, however, at Cd2+ concentrations higher than 12.5 microM the respiratory activation became short-term with a following reduction in respiration. Cd2+ influence on respiration of mitochondria increased in the medium with NaCl, which resulted in decreasing the acting Cd2+ concentrations and in activating state 4 respiration more intensely. Cd2+ did not modify respiration of mitochondria in the experiments with LiCl in the medium, except that Cd2+ in concentrations higher than 10 microM decreased the state 4 respiration mitochondria just as in NaCl experiments. On the contrary, Cd2+ influence on respiration of mitochondria was seen decreased in the medium with sucrose. This was displayed in the increase in Cd2+ acting concentrations and in the decrease in activation of state 4 respiration mitochondria, and is associated with the nonosmotic character of these effects. On 20 microM Cd2+ concentration only, an extensive swelling of nonenergized mitochondria was observed in 12.5 mM nitrate media and its increase in series of LiNaKNH4. The initially low swelling of succinate energized mitochondria in KCl medium was increased at raising Cd2+ concentration in this medium. A non-uniform Cd2+ influence on respiration and mitochondrial swelling in the above incubated media may be firstly associated with different effects of K+, Na+, Li+ and sucrose on membrane ion permeability and on Cd+ binding with the membrane, and, secondly, correlated with the action of medium components on energy dependent Cd2+ uptake by mitochondria and on Cd2+ penetration to mitochondrial respiratory enzymes.

Cadmium inhibits many mitochondrial enzymes participating in respiratory and oxidative phosphorylation processes, with reactive SH-groups of some of these enzymes being localized in hydrophobic domains of mitochondrial membrane. A comparative investigation was made of the action of Cd2+ and two its hydrophobic complexes (a more hydrophobic one with 1, 3-bis(4-chlorbenzilidenamino) guanidine [Cd(CBG)], and a less hydrophobic one with anabazin [Cd(ANB)] on ion permeability of the mitochondrial membrane and on respiration of rat liver mitochondria in vitro. Cd2+ ions in concentration of more than 2.5 microM and in the presence of DNP decreased mitochondrial respiration in state 3 and activated in in state 4; however, in concentration higher than 20 microM Cd2+ the activation acquired a short-term character and the state 4 respiration was seen to decrease. The experiments on mitochondrial swelling in the medium containing 125 mM NH4NO3 revealed that the complex and CBG, like Cd2+, increased proton permeability of the internal mitochondrial membrane. 10 microM Cd(ANB) and Cd(CBG) had more effect on mitochondrial respiration than Cd2+ CBG (in DNP-stimulated respiration), and ANB had no effect on mitochondrial respiration. The toxicity of Cd(CBG) was higher than that of Cd2+ and Cd(ANB), due to a higher hydrophobicity of Cd(CBG). A higher activity of Cd(CBG) was suggested to be due to its hydrophobicity. In the experiments with 137Cs in succinate-energized mitochondria at 20 degrees C and 10(-8) valinomycine, the susceptibility of toxic effects caused by the complex was lower than that caused by Cd2+ in the presence of ruthenium red, which is a blocker of Ca2+ transport. A higher Cd(CBG) effect in experiments with 137Cs and RR is accounted for by the fact that these agents are transported into mitochondria via different pathways. On the contrary, the effect of RR in similar experiments with Cd(ANB) was stronger than that of Cd2+. It is assumed that transport of Cd(ANB) in mitochondria, opposite to that of Cd(CBG), is not carried out across hydrophobic domains of the mitochondrial membrane.

Action of Cd+ on mitochondrial respiration is decreased by some bivalent ions, however the reason of this still remains obscure. Change of Cd2+ action over a wide range of its concentrations on respiration of rat liver mitochondria in states 4, 3 and in the presence of 2, 4-dinitrophenol (DNP) after mitochondrial preincubation with Ca2+, Sr2+, Ba2+, Mn2+ or ruthenium Red (RR) was studied in vitro. In the control (experiments without preincubation), Cd2+ lowers mitochondrial respiration in state 3 as well as that in the presence of DNP, and increases the respiration in state 4. However, the respiration is decreased if Cd2+ concentrations are more than 15 microM; in this case a short-term activation of respiration appears. In comparison with the control, it was demonstrated that the action of Cd2+ on mitochondrial respiration was enhanced in experiments with Ca2+, decreased in experiments with Sr2+ and Mn2+, and did not vary practically in experiments with Ba2+. The activation of respiration in state 4 is increased in experiments with Ca2+ and is absent with Mn2+. Different changes in Cd2+ action on mitochondrial respiration in experiments with Me2+ ions are associated with their influence on mitochondrial membrane permeability, as well as with magnitude of the ion radius. The maximum reduce of Cd2+ action was achieved in experiments with RR, except that respiration in state 3 decreased by Cd2+ to 30 microM more rapidly than with Sr2+ and Mn2+. Under RR experiments the mitochondrial respiration in the presence of DNP as well as that in state 3 is linearly decreased (up to 15 microM Cd2+). A discussion involves issues of Cd2+ transport into the matrix, under uniporter blocking, as well as inorganic phosphate influence on Cd2+ effects, location of regulatory centers of ion permeability and location of active group of respiration enzymes.