V. P. Nesterov

Effects of pinacidil and calcium on isolated rat heart mitochondria

113 It was shown in [1–3] that pinacidil, a nonselective modulator of mitochondrial K ATP dependent chann nels (mitoK ATP), had a pronounced protective effect on the contractile parameters of an isolated rat heart after exposure to ischemia and subsequent reperfuu sion. This protective effect of pinacidil and diazoxide, a selective modulator of these channels, was termed pharmacological preconditioning [3]. To date, there is no single point of view on the nature of this phenomee non [2, 4–8]. Some researchers believe that activation of mitochondrial K ATP dependent channels by pinacii dil triggers a complex cascade mechanism of preconn ditioning involving protein kinase C. Others believe that this protective effect of pinacidil is determined by its ability for mild uncoupling of respiration of mitoo chondria. This, in turn, facilitates their swelling, stimm ulates reduction of electrochemical potential (ΔΨ mito) on the inner mitochondrial membrane (IMM), and ultimately reduces the voltageedependent accumulaa tion of calcium in the matrix after exposure of the heart to ischemia/reperfusion. Pinacidil was shown to activate respiration of isoo lated mitochondria in states 2 and 4 [1, 3, 9–13]. However, mitochondrial respiration in state 3 and the ATP synthesis rate are changed only slightly [9, 13]. Pinacidil decreases calcium transport to the matrix and stimulates swelling of mitochondria and the proo ton permeability of their inner membrane [1, 3, 8, 12]. It is known that mitochondrial calcium load followed by reduction of ΔΨ mito may lead to the opening of the mitochondrial permeability transition pore (MPTP) in the inner mitochondrial membrane [7, 14]. In recent years, the relationship between the structural elements that form mitoK ATP and MPTP is widely diss cussed [6, 7]. It was shown that pinacidil prevents the opening of the MPTP in cardiomyocytes loaded with tetramethylrhodamine methyl ester (TMRM) [15]. Given the above, it is clear that the relationship of the effects of pinacidil with the MPTP induction in the inner membrane of mitochondria under conditions of calcium load has almost not been studied. For this reaa son, we investigated the combined effect of pinacidil (a mild uncoupling agent) and calcium on the swelll ing, respiration, and membrane potential of isolated rat heart mitochondria. Experiments were performed with male Wistar rats weighing 200–250 g. Rat heart mitochondria (RHM) were isolated by the method developed by us earlier [4] and suspended in 3 mL of a medium containing 300 mM sucrose and 10 mM …

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.

Effects of lithium on isolated rat heart mitochondria.

S state 4, state 3, and 2,4-dinitrophenol (DNP)-stimulated respiration as well as the membrane potential (Ψmito) of Li+-loaded rat heart mitochondria (LiRHM) were studied. The Li+ loading of rat heart mitochondri a (RHM) resulted both in increase of passive permeability of the inner mitochondrial membrane (IMM) to H+ or K+ ions and in decrease of activity of the mitochondrial Na+/H+ exchanger. In comparison to RHM, energized LiRHM weaker pumped out protons from the matrix and demonstrated more potent uptake of K+ from an incubation medium. State 3 and 2,4-dinitrophenol (DNP)-stimulated respiration as well as the membrane potential (∆Ψmito) of LiRHM in KCl or LiCl media were the same that the parameters found in experiments with RHM. It is supposed that negligible influence of Li+ on the respiration can be possible resulted in that Li+ unlike Na+ does not decrease activity of mitochondrial respiratory enzymes. It is discussed that diminution of contractile parameters of heart preparations after replacement in Ringer solution of NaCl by LiCl can be related to influence of LiCl on trigger extension in cardiac musle but not to effects of LiCl on energy supply of exitation-contraction processes in a heart. Effects of Li+ on isolated rat heart mitochondria

Evolutionary Aspects of Cardioprotection

The review addresses the mechanisms of adaptation of the myocardium and cells of the cardiovascular system to hypoxia and ischemia as well as biochemical mechanisms of cardioprotection in animals of different phylogenetic levels. A special focus is placed on general adaptive strategies developed by evolutionarily distant animals in response to hypoxia and ischemia and on preconditioning and myocardial hibernation phenomena.

Mersalyl prevents the Tl + -induced permeability transition pore opening in the inner membrane of Ca 2+ -loaded rat liver mitochondria

It was earlier shown that the calcium load of rat liver mitochondria in medium containing TlNO3 and KNO3 resulted in the Tl+-induced mitochondrial permeability transition pore (MPTP) opening in the inner membrane. This opening was accompanied by an increase in swelling and membrane potential dissipation and a decrease in state 3, state 4, and 2,4-dinitrophenol-uncoupled respiration. This respiratory decrease was markedly leveled by mersalyl (MSL), the phosphate symporter (PiC) inhibitor which poorly stimulated the calcium-induced swelling, but further increased the potential dissipation. All of these effects of Ca2+ and MSL were visibly reduced in the presence of the MPTP inhibitors (ADP, N-ethylmaleimide, and cyclosporine A). High MSL concentrations attenuated the ability of ADP to inhibit the MPTP. Our data suggest that the PiC can participate in the Tl+-induced MPTP opening in the inner membrane of Ca2+-loaded rat liver mitochondria.

Involvement of Ca2+ in the development of ischemic disorders of myocardial contractile function

The review addresses the role of Ca2+ ions in the development of ischemic disorders of myocardial contractility associated with changes in Ca2+ homeostasis in cardiomyocytes and mitochondrial Ca2+ overload. A special attention is paid to the analysis of intracellular signaling mechanisms activated during the development of ischemic and reperfusion injury of the myocardium.

The effects of Tl+ ions on the dynamics of intracellular Ca2+ in rat cardiomyocytes

The effects of Т1+ ions on the dynamics of intracellular Cа2+ in neonatal rat cardiomyocytes have been studied. It was shown for the first time that application of Т1+ led to an uncontrolled increase in [Cа2+]i in cells. Moreover, the ability of Т1+ to increase [Cа2+]i depended on the Т1+ concentration used and the time of exposure to the cells. The increase in [Cа2+]i was related to the entry of Cа2+ from the extracellular medium. Thallium did not release Cа2+ from intracellular stores. The thallium-induced increase in [Cа2+]i was not inhibited by nifedipine. It is possible that L-channels do not participate in the processes of thalliuminduced increase in [Cа2+]i. It is assumed that the thallium ions-induced calcium overload in cardiomyocytes may contribute to the toxic effect of Т1+ on the myocardium.

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 Pr3+ and La3+ ions on the heart muscle of frog Rana ridibunda, as well as the influence of the ions on respiration, swelling, and the potential (ΔΨmito) on the inner membrane of Ca2+- loaded rat heart mitochondria, energized by glutamate and malate or succinate in the presence of rotenone were studied. It was found that 2 mM Pr3+ 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. Pr3+ and La3+ 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 ΔΨmito on the inner mitochondrial membrane that were induced by Ca2+ ions. Retardation by Pr3+ and La3+ 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 Ca2+ 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 Ca2+-dependent processes in the vertebrate myocardium.