Tag Archives: Ca2+

Influence of Tl(+) on the Ca(2+) and Na(+) movement across rat neonatal cardiomyocytes and rat heart mitochondria membranes

S. M. Korotkov, V. P. Nesterov, G. B. Belostotskaya,
I. V. Brailovskaya, A. V. Novozhilov, C. V. Sobol

Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russian Federation;
e-mail: korotkov@SK1645.spb.edu

Received: 05 September 2019; Accepted: 29 November 2019

Thallium is known to produce one of the most complex and serious patterns of toxicity, involving a wide range of human organs and tissues. The toxic impact on biologic organisms is linked especially to the ability of Tl+ to disturb calcium homeostasis and  to permeate easily the inner mitochondrial membrane (IMM). The aim of this work was to study the effects of Tl+ on intracellular Ca2+ dynamics in rat neonatal cardiomyocytes as well as on sodium penetrability of the IMM and Tl+-induced mitochondrial permeability transition pore (MPTP) opening in isolated Ca2+-loaded rat heart mitochondria (RHM). The use of the fluorescent calcium indicator Fura 2 AM showed that Tl+ induced calcium influx across the plasmatic membrane, resulting­ in calcium ([Ca2+]i) increase in the cytoplasm. This increase was even more pronounced in experiments with accelerating of Tl+-transmembrane fluxes by nonactin. It was nevertheless abolished by the removal of extracellular Ca2+ ions, but was not inhibited by a calcium-channel blocker (nifedipine). Tl+ did not release calcium from the intracellular stores. Tl+ potentiated sodium permeability of the IMM because swelling of nonenergized RHM in medium containing TlNO3 and NaNO3 was enhanced at high Tl+ concentration. The calcium load of RHM induced MPTP opening which was accompanied by the increase of the swelling as well as the decrease of  the inner membrane potential and of state 40 (basal) and state 3UDNP (2,4-dinitrophenol-uncoupled) respiration. These effects of Tl+ were suppressed by MPTP inhibitors (cyclosporine A, ADP and n-ethylmaleimide). The data obtained showed that Tl+-stimulated influx of extracellular calcium into cardiomyocytes could cause calcium and sodium RHM overload, which lead to the MPTP opening, thus determining the sensitivity of heart muscle to thallium intoxication.

Transmembrane Ca(2+) exchange in depolarized rat myometrium mitochondria

L. G. Babich, S. G. Shlykov, N. V. Kandaurova, S. A. Kosterin

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: babich@biochem.kiev.ua

Polarization of the inner membrane is the key factor in maintenance of the physiologically significant cations accumulation, in particular Ca2+, in the mitochondria. It has been well established that mitochondria accumulate calcium through the uniporter, driven by the mitochondrial membrane potential.  Nevertheless, it has been shown that depolarized mitochondria also accumulate Ca2+. The aim of this paper is to investigate free Ca level in depolarized myometrium mitochondria. As we have shown previously Ca2+ addition to the incubation medium, that did not contain K-phosphate, ATP and Mg2+, led to inner mitochondrial membrane depolarization. Nevertheless Ca2+ addition to such medium led to the concentration-dependent accumulation of this cation in the matrix. RuR or Mg addition to the incubation medium led to the higher elevation of mitochondrial Ca2+ level in depolarized mitochondria. Mitochondrial Ca2+ level was not affected by 5 µM cyclosporine A. It was suggested that Н+/Са2+ exchanger could provide calcium accumulation in depolarized mitochondria. The elevation of mitochondrial Ca2+ level after addition of Mg2+ and RuR may be due to inhibition of Ca2+ efflux through Ca2+ uniporter.

Nicotine effects on mitochondria membrane potential: participation of nicotinic acetylcholine receptors

G. L. Gergalova, M. V. Skok

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: gergal71@gmail.com

The effect of nicotine on the mouse liver mitochondria was studied by fluorescent flow cytometry. Mice consumed nicotine during 65 days; alternatively, nicotine was added to isolated mitochondria. Mitochondria of nicotine-treated mice had significantly lower basic levels of membrane potential and granularity as compared to those of the control group. Pre-incubation of the isolated mitochondria with nicotine prevented from dissipation of their membrane potential stimulated with 0.8 µM СаСl2 depending on the dose, and this effect was strengthened by the antagonist of α7 nicotinic receptors (α7 nAChR) methyllicaconitine. Mitochondria of mice intravenously injected with the antibodies against α7 nAChR demonstrated lower levels of membrane potential. Introduction of nicotine, choline, acetylcholine or synthetic α7 nAChR agonist PNU 282987 into the incubation medium inhibited Ca2+ accumulation in mitochondria, although the doses of agonists were too low to activate the α7 nAChR ion channel. It is concluded that nicotine consumption worsens the functional state of mitochondria by affecting their membrane potential and granularity, and this effect, at least in part, is mediated by α7 nAChR desensitization.

The influence of ATP-dependent K(+)-channel diazoxide opener on the opening of mitochondrial permeability transition pore in rat liver mitochondria

O. V. Akopova

Bogomolets Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv;
e-mail: luko@biph.kiev.ua

The influence of mitochondrial ATP-dependent­ K+-channel (K+АТР-channel) opener, diazoxide (DZ) on the mitochondrial permeabili­ty transition pore (MPTP) opening in rat liver mitochondria is studied. In the absence of DZ the MPTP opening leads to the increase in the rate of K+– and Ca2+-cycling supported by the simultaneous functioning of K+-channels and K+/H+-antiporter, and also Ca2+-uniporter together with MPTP as the cations influx and efflux pathways. Independent of MPTP opening, the activation of both constitutes of K+-cycle, K+-uptake as well as K+/H+-exchange, by DZ is observed. It is shown that the activation of transmembrane exchange of K+, combined with MPTP opening, results in partial inhibition of the latter. A simple methodical approach for the estimation of DZ influence on the open state of mitochondrial pore is proposed.
It is shown that MPTP closure followed by Ca2+ reentry to the matrix is accompanied by the K+/H+-exchange inhibition which takes place in the same timeframes as the increase in matrix Ca2+ content. Relevant to physiological conditions, an important physiological function of MPTP is revealed, that is the maintenance of relatively low matrix level of Ca2+ accompanied by the acceleration of transmembrane ion exchange (K+ and Ca2+) which could strongly influence the energy state and energy-dependent processes in mitochondria.

Influence of Са(2+) on kinetic parameters of pancreatic acinar mitochondria in situ respiration

B. O. Manko, V. V. Manko

Ivan Franko National University of Lviv, Ukraine;
e-mail: mankobo@gmail.com

The dependence of respiration rate of rat permeabilized acinar pancreacytes on oxidative substrates concentration was studied at various [Ca2+] – 10-8–10-6 M. Pancreacytes were permeabilized with 50 µg of digitonin per 1 million cells. Respiration rate was measured polarographically using the Clark electrode at oxidation of succinate or pyruvate either glutamate in the presence of malate. Parameters of Michaelis-Menten equation were calculated by the method of Cornish-Bowden or using Idi-Hofsti coordinates and parameters of Hill equation – using coordinates {v; v/[S]h}. In the studied range of [Ca2+] the kinetic dependence of respiration at pyruvate oxidation is described by the Michaelis-Menten equation, and at oxidation of succinate or glutamate – by Hill equation with h = 1.11–1.43 and 0.50–0.85, respectively. The apparent constant of respiration half-activation (K0.5) did not significantly change in the studied­ range of [Ca2+] while at 10-7 M Ca2+ it was 0.90 ± 0.06 mM for succinate, 0.096 ± 0.007 mM for pyruvate and 0.34 ± 0.03 mM for glutamate. Maximum respiration rate Vmax at pyruvate oxidation increased from 0.077 ± 0.002 to 0.119 ± 0.002 and 0.140 ± 0.002 nmol O2/(s·million cells) due to the increase of [Ca2+] from 10-7 to 5×10-7 or 10-6 M, respectively. At oxidation of succinate or glutamate Ca2+ did not significantly affect Vmax. Thus, the increase of [Ca2+] stimulates respiration of mitochondria in situ of acinar pancreacytes at oxidation of exogenous pyruvate (obviously due to pyruvate dehydrogenase activation), but not at succinate or glutamate oxidation.

Calmodulin antagonists effect on Ca(2+) level in the mitochondria and cytoplasm of myometrium cells

S. G. Shlykov, L. G. Babich, M. E. Yevtushenko, S. O. Karakhim, S. O. Kosterin

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: sshlykov@biochem.kiev.ua

It is known that Са2+-dependent regulation of this cation exchange in mitochondria is carried out with participation of calmodulin. We had shown in a previous work using two experimental models: isolated mitochondria and intact myometrium cells, that calmodulin antagonists reduce the level of mitochondrial membrane polarization. The aim of this work was to investigate the influence of calmodulin antagonists on the level of ionized Са in mitochondria and cytoplasm of uterine smooth muscle cells using spectrofluorometry and confocal microscopy. It was shown that myometrium mitochondria, in the presence of АТР and MgCl2 in the incubation medium, accumulate Са ions in the matrix. Incubation of mitochondria in the presence of СССР inhibited cation accumulation, but did not cease it. Calmodulin antagonist such as trifluoperazine (100 µМ) considerably increased the level of ionized Са in the mitochondrial matrix. Preliminary incubation of mitochondria with 100 µМ Са2+, before adding trifluoperazine to the incubation medium, partly prevented influence of the latter on the cation level in the matrix. Incubation of myometrium cells (primary culture) with another calmodulin antagonist calmidazolium (10 µМ) was accompanied by depolarization of mitochondrial membrane and an increase in the concentration of ionized Са in cytoplasm. Thus, using two models, namely, isolated mitochondria and intact myometrium cells, it has been shown that calmodulin antagonists cause depolarization of mitochondrial membranes and an increase of the ionized Са concentration in both the mitochondrial matrix and the cell cytoplasm.

Kinetics of inhibitory effect of calix[4]arene С-90 on activity of transporting plasma membrane Cа(2+),Mg(2+)-ATPase of smooth muscle cells

T. O. Veklich1, A. A. Shkrabak1, Yu. Yu. Mazur1,
R. V. Rodik2, V. I. Kalchenko2, S. O. Kosterin1

1Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
2Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: kinet@biochem.kiev.ua; vik@ioch.kiev.ua

In experiments on the suspension of myometrium cell plasma membrane, processed by 0.1% digitonin, the inhibitory action of calix[4]arene C-90 (5,11,17,23-tetra(threeftor)methyl(phenilsulphonilimino)-methylamino-25,26, 27,28-tetrapropoxy-calix[4]arene) on the activi­ty of Ca2+,Mg2+-ATPase was investigated. The authors also examined the influence of calix[4]arene in different concentration on affinity of enzyme (Ca2+,Mg2+-ATPase) for the ATP and ions of Mg and Ca, and its influence on cooperative effect and maximum velocity of ATP hydrolysis. It is shown that calix[4]arene does not influence the affinity of Ca2+,Mg2+-ATPase for the ATP, which means that these two compounds have different binding centers­. Also calix[4]arene has no influence on affinity and cooperative effect of Ca ions, if it is used in concentration lower than 50 µM. Calix[4]arene slightly increases coefficient of Ca2+,Mg2+-ATPase activation by magnesium chloride. In all three cases, where ATP, Mg and Ca ions are used to test the impact of calix[4]arene, maximum velocity of ATP hydrolysis significantly decreases. All these results clarify that calix[4]arene implements its inhibitory action through mechanism of uncompetitive inhibition of Ca2+,Mg2+-ATPase activity.

Activation of glybenclamide-sensitive mitochondrial swelling under induction of cyclosporin of A-sensitive mitochondrial pore

O. B. Vadzyuk, S. A. Kosterin

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: olga_vadzyuk@hotmail.com

Induction of mitochondrial swelling and increased generation of reactive oxygen forms by Ca ions have been shown in suspension of mitochondria from rat uterus. These effects were suppressed by the blocker of mitochondrial Ca2+-uniporter ruthenium red and MPTP inhibitor сyclosporin A, that evidences that the induction of mitochondrial permeability transition pore by Ca ions takes place. Ca2+-induced mitochondrial swelling was blocked by ATP-sensitive channel blocker glybenclamide but only if K+ was present in the incubation medium. We also demonstrated that Ca2+-induced mitochondrial swelling can be eliminated in the presence of ROS scavengers N-acetyl cysteine and ascorbate. This effect of scavengers was also sensitive to K+ and was not revealed in the medium that contained equimolar NaCl instead of KCl. Thus, our data gave us grounds to assume that the induction of MPTP by Ca ions evokes the activation of mitochondrial ATP-sensitive K+-channels, which are mediated by ROS.