A comparative study of the effects of Pr3+ and La3+ ions on calcium dependent processes in frog cardiac muscle and rat heart mitochondria

The inotropic effect of Pr 3+ and La 3+ ions on the heart muscle of frog Rana ridibunda , as well as the influence of the ions on respiration, swelling, and the potential (ΔΨ mito ) on the inner membrane of Ca 2+ - loaded rat heart mitochondria, energized by glutamate and malate or succinate in the presence of rotenone were studied. It was found that 2 mM Pr 3+ in Ringer’s solution reduces the force of spontaneous contractions and those induced by electrical stimulation in the heart; it had a negative chronotropic effect, decreasing the frequency of spontaneous contractions. Pr 3+ and La 3+ prevented a decrease in the 2,4-dinitrophenol (DNP)- uncoupled respiration of energized rat heart mitochondria, swelling of these organelles in salt media, and a reduction in ΔΨ mito on the inner mitochondrial membrane that were induced by Ca 2+ ions. Retardation by Pr 3+ and La 3+ ions of these calcium-induced effects may suggest that in the inner mitochondrial membrane these metals inhibit the opening of the mitochondrial permeability transition pore caused by Ca 2+ overload of mitochondria. The data we obtained are important for a better understanding of the mechanisms of the damaging action of rare-earth elements on Ca 2+ -dependent processes in the vertebrate myocardium.