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Inoptopic effect of yttrium acetate (Y 3+ ) on myocardium of the marsh frog Rana ridibunda and its effect on ion transport across the inner mitochondrial membrane (IMM) of rat heart was studied. Y 3+ was found to decrease the rate of heart contractions and to stimulate ion transport in the rat heart mitochondria in media with 10 mM glutamate and 2 mM malate. Presence of Y 3+ induced inhibition of energy-dependent Ca 2+ transport into mitochondria, which was expressed as a marked decrease of their swelling in the media containing 125 mM NH 4 NO 3 and Ca 2+ or 25 mM potassium acetate, 100 mM sucrose and Ca 2+ . It is suggested that the Y 3+ -induced decrease in rat muscle contractions is determined not only by direct suppressing effect of Y 3+ on potential-modulated Са 2+ -channels of pacemaker and contractile cardiomyocytes (CM), but also by its indirect effect on Са 2+ -carrier in IMM. The data confirming that Y 3+ activates energy-dependent K + transport catalyzed by mitochondrial uniporter and blocks Ca 2+ -channels in the mitochondrial membrane are important for more complete understanding of mechanisms of the Y 3+ action on vertebrates and human CM.

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