[COMPARATIVE STUDY OF Y³⁺ EFFECT ON CALCIUM-DEPENDENT PROCESSES IN FROG CARDIAC MUSCLE AND IN MITOCHONDRIA OF RAT CARDIOMYOCYTES].

Inotropic effects of yttrium acetate (Y³⁺) on contractions of myocardium preparations of the frog Ra- na ridibunda as well as on respiration and the inner membrane potential (Δψmito) of isolated rat heart mi- tochondria were studied. It was found that 2 mM yttrium in Ringer solution significantly reduced the am- plitude of myocardium contractions evoked by electric stimulation and increased the half-relaxation time (n = 5). In experiments with Ca²⁺, Y³⁺ decreased Ca²⁺-dependent oxygen consumption rate of rat heart mitochondria, energized by glutamate and malate, impeded the reduction in respiration of these mito- chondria in state 3 or uncoupled by 2,4-dinitrophenol, and inhibited Ca²⁺-induced decrease in their inner membrane potential. These data are important to better understand the mechanisms of Y³⁺ effects on myocardial calcium-dependent processes. Possible mechanisms of negative inotropic effect of Y³⁺ on the myocardium and its influence on the Ca²⁺-dependent processes in rat mitochondria are discussed.