Comparative study of Y3+ effect on calcium-dependent processes in frog cardiac muscle and mitochondria of rat cardiomyocytes

Inotropic effects of yttrium acetate (Y3+) on contractions of myocardium preparations of the frog Rana ridibunda, as well as on respiration and the inner membrane potential (ΔΨmito) of isolated rat heart mitochondria were studied. 2 mM yttrium in Ringer solution was found to significantly reduce the amplitude of myocardium contractions, evoked by electric stimulation, and increase the half-relaxation time (n = 5). In experiments with Ca2+, Y3+ decreased the Ca2+-dependent basal respiration rate in rat heart mitochondria, energized by glutamate and malate, impeded the reduction in respiration of these mitochondria operating in state 3 after Chance or uncoupled by 2,4-dinitrophenol, and inhibited a Ca2+-induced reduction in their inner membrane potential. The data obtained are important for better understanding the mechanism underlying Y3+ effects on the myocardial Ca2+-dependent processes. Possible mechanisms of the negative inotropic effect of Y3+ on myocardium and its influence on the Ca2+-dependent processes in rat mitochondria are discussed.