Mersalyl prevents the Tl+-induced permeability transition pore opening in the inner membrane of Ca2+-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.     

Tl+ induces both cationic and transition pore permeability in the inner membrane of rat heart mitochondria

Effects of Tl⁺ were studied in experiments with isolated rat heart mitochondria (RHM) injected into 400 mOsm medium containing TlNO₃ and a nitrate salt (KNO₃ or NH₄NO₃) or TlNO₃ and sucrose. Tl⁺ increased permeability of the inner membrane of the RHM to K⁺ and H⁺. This manifested as an increase of the non-energized RHM swelling, in the order of sucrose < K⁺ < NH₄ ⁺, respectively. After succinate administration, the swollen RHM contracted. The Tl⁺-induced opening of the mitochondrial permeability pore (MPTP) in Ca²⁺-loaded rat heart mitochondria increased both the swelling and the inner membrane potential dissipation, as well as decreased basal state and 2,4-dinitrophenol-stimulated respiration. These effects of Tl⁺ were suppressed by the MPTP inhibitors (cyclosporine A, ADP, bongkrekic acid, and n-ethylmaleimide), activated in the presence of the MPTP inducer (carboxyatractyloside) or mitoK_ATP inhibitor (5-hydroxydecanoate), but were not altered in the presence of mitoK_ATP agonists (diazoxide or pinacidil). We suggest that the greater sensitivity of heart and striated muscles, versus liver, to thallium salts in vivo can result in more vigorous Tl⁺ effects on muscle cell mitochondria.     

A comparative study of the effects of Pr<Superscript>3+</Superscript> and La<Superscript>3+</Superscript> 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 (ΔΨ_mito) 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 ΔΨ_mito 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.     

Effects of Tl<Superscript>+</Superscript> on ion permeability,membrane potential and respiration of isolated rat liver mitochondria

It is known that permeability of the inner mitochondrial membrane is low to most univalent cations (K⁺, Na⁺, H⁺) but high to Tl⁺. Swelling, state 4, state 3, and 2,4-dinitrophenol (DNP)-stimulated respiration as well as the membrane potential (ΔΨ_mito) of rat liver mitochondria were studied in media containing 0–75 mM TlNO₃ either with 250 mM sucrose or with 125 mM nitrate salts of other monovalent cations (KNO₃, or NaNO₃, or NH₄NO₃). Tl⁺ increased permeability of the inner mitochondrial membrane to K⁺, Na⁺, and H⁺, that was manifested as stimulation of the swelling of nonenergized and energized mitochondria as well as via an increase of state 4 and dissipation of ΔΨ_mito. These effects of Tl⁺ increased in the order of sucrose <K⁺ <Na⁺ ≤ NH₄⁺. They were stimulated by inorganic phosphate and decreased by ADP, Mg²⁺, and cyclosporine A. Contraction of energized mitochondria, swollen in the nitrate media, was markedly inhibited by quinine. It suggests participation of the mitochondrial K⁺/H⁺ exchanger in extruding of Tl⁺-induced excess of univalent cations from the mitochondrial matrix. It is discussed that Tl⁺ (like Cd²⁺ and other heavy metals) increases the ion permeability of the inner membrane of mitochondria regardless of their energization and stimulates the mitochondrial permeability transition pore in low conductance state. The observed decrease of state 3 and DNP-stimulated respiration in the nitrate media resulted from the mitochondrial swelling rather than from an inhibition of respiratory enzymes as is the case with the bivalent heavy metals.     

Effect of bedaquiline on the functions of rat liver mitochondria

The paper considers the effects of bedaquiline (BDQ), an antituberculous preparation of the new generation, on rat liver mitochondria. It was shown that 50?μM BDQ inhibited mitochondrial respiration measured with substrates of complexes I and II (glutamate/malate and succinate/rotenone systems respectively) in the states V₃ and V_DNP. At the same time, at concentrations below 50?μM, BDQ slightly stimulated respiration with substrates of complex I in the state V₂. BDQ was also found to suppress, in a dose-dependent manner, the activity of complex II and the total activity of complexes II?+?III of the mitochondrial transport chain. It was discovered that at concentrations up to 10?μM, BDQ inhibited H₂O₂ production in mitochondria. BDQ (10–50?μM) suppressed the opening of Ca²⁺-dependent CsA-sensitive mitochondrial permeability transition pore. The latter was revealed experimentally as the inhibition of Ca²⁺/P_i-dependent swelling of mitochondria, suppression of cytochrome c release, and an increase in the Ca²⁺ capacity of the organelles. BDQ also decreased the rate of mitochondrial energy-dependent K⁺ transport, which was evaluated by the energy-dependent swelling of mitochondria in a K⁺ buffer and DNP-induced K⁺ efflux from the organelles. The possible mechanisms of BDQ effect of rat liver mitochondria are discussed.     

Dietary supplementation with docosahexaenoic acid, but not eicosapentaenoic acid, dramatically alters cardiac mitochondrial phospholipid fatty acid composition and prevents permeability transition

Treatment with the ω-3 polyunsaturated fatty acids (PUFAs) docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) exerts cardioprotective effects, and suppresses Ca²⁺-induced opening of the mitochondrial permeability transition pore (MPTP). These effects are associated with increased DHA and EPA, and lower arachidonic acid (ARA) in cardiac phospholipids. While clinical studies suggest the triglyceride lowering effects of DHA and EPA are equivalent, little is known about the independent effects of DHA and EPA on mitochondria function. We compared the effects of dietary supplementation with the ω-3 PUFAs DHA and EPA on cardiac mitochondrial phospholipid fatty acid composition and Ca²⁺-induced MPTP opening. Rats were fed a standard lab diet with either normal low levels of ω-3 PUFA, or DHA or EPA at 2.5% of energy intake for 8 weeks, and cardiac mitochondria were isolated and analyzed for Ca²⁺-induced MPTP opening and phospholipid fatty acyl composition. DHA supplementation increased both DHA and EPA and decreased ARA in mitochondrial phospholipid, and significantly delayed MPTP opening as assessed by increased Ca²⁺ retention capacity and decreased Ca²⁺-induced mitochondria swelling. EPA supplementation increased EPA in mitochondrial phospholipids, but did not affect DHA, only modestly lowered ARA, and did not affect MPTP opening. In summary, dietary supplementation with DHA but not EPA, profoundly altered mitochondrial phospholipid fatty acid composition and delayed Ca²⁺-induced MPTP opening.     

Bile Acid-Induced Ca<Superscript>2+</Superscript> Efflux from Liver Mitochondria as a Factor Preventing the Formation of Mitochondrial Pores

The effect of bile acids as inducers of Ca²⁺ efflux from the matrix was studied on isolated rat liver mitochondria. Mitochondria in the presence of cyclosporin A (CsA) were energized by succinate, then loaded with Ca²⁺ and after the addition of the calcium uniporter inhibitor ruthenium red were de-energized by malonate. It was shown that under these conditions hydrophobic bile acids lithocholic and chenodeoxycholic at concentrations of 10 and 30 μM respectively and hydrophilic bile acids ursodeoxycholic and cholic at a concentration of 400 μM induce Ca²⁺ efflux from the mitochondrial matrix. It is noted that the efflux of these ions is not associated with damage of the inner mitochondrial membrane by bile acids, since it is accompanied by the generation of Δψ, i.e., the formation of the diffusion potential. It is assumed that along with induction of calcium efflux from the matrix, bile acids are also capable of transporting hydrogen and potassium ions in the opposite direction, i.e., perform H⁺/Ca²⁺ and K⁺/Ca²⁺ exchange. It was found that ruthenium red added to Ca²⁺-loaded energized mitochondria prevents the return of these ions to the matrix and weakens the effect of chenodeoxycholic acid as an inducer of the CsA-sensitive mitochondrial pore and the effect of ursodeoxycholic acid as an inducer of CsA-insensitive permeability of the inner mitochondrial membrane. We conclude that in the conditions of the calcium uniporter activity decrease, Ca²⁺ efflux from the matrix induced by bile acids can be considered as one of the mechanisms reducing their effectiveness as inducers of the Ca²⁺-dependent CsA-sensitive pore and CsA-insensitive permeability transition in mitochondria.     

Diacylglycerols Activate Mitochondrial Cationic Channel(s) and Release Sequestered Ca<Superscript>2+</Superscript>

Mitochondria contribute to cytosolic Ca²⁺ homeostasis through several uptake and release pathways. Here we report that 1,2-sn-diacylglycerols (DAGs) induce Ca²⁺ release from Ca²⁺-loaded mammalian mitochondria. Release is not mediated by the uniporter or the Na⁺/Ca²⁺ exchanger, nor is it attributed to putative catabolites. DAGs-induced Ca²⁺ efflux is biphasic. Initial release is rapid and transient, insensitive to permeability transition inhibitors, and not accompanied by mitochondrial swelling. Following initial rapid release of Ca²⁺ and relatively slow reuptake, a secondary progressive release of Ca²⁺ occurs, associated with swelling, and mitigated by permeability transition inhibitors. The initial peak of DAGs-induced Ca²⁺ efflux is abolished by La³⁺ (1 mM) and potentiated by protein kinase C inhibitors. Phorbol esters, 1,3-diacylglycerols and 1-monoacylglycerols do not induce mitochondrial Ca²⁺ efflux. Ca²⁺-loaded mitoplasts devoid of outer mitochondrial membrane also exhibit DAGs-induced Ca²⁺ release, indicating that this mechanism resides at the inner mitochondrial membrane. Patch clamping brain mitoplasts reveal DAGs-induced slightly cation-selective channel activity that is insensitive to bongkrekic acid and abolished by La³⁺. The presence of a second messenger-sensitive Ca²⁺ release mechanism in mitochondria could have an important impact on intracellular Ca²⁺ homeostasis.     

Mechanism of mitochondrial transport of thallous ions

Rat liver mitochondria were found to swell under nonenergized conditions when suspended in media containing 30–40 mM TINO₃. Respiration on succinate caused a rapid contraction of mitochondria swollen under nonenergized conditions. In the presence of thallous acetate, there was a rapid initial swelling under nonenergized conditions until a plateau was reached; respiration on succinate then caused a further swelling. Trace amounts of²⁰⁴Tl (less than 100 µM) equilibrated fairly rapidly across the mitochondrial membrane. The influx of Tl⁺ was able to promote the decay not only of a valinomycin-induced K⁺-diffusion potential but also of respiration-generated fields in the inner membrane in accordance with the electrophoretic nature of Tl⁺ movement. Efflux of Tl⁺ showed a half-time of about 10 sec at 20°C and was not affected appreciably by the energy state. Efflux was retarded by Mg²⁺ and by lowering the temperature. The data indicate that Tl⁺ when present at high concentrations, 30 mM or more, distributes across the mitochondrial inner membrane both in response to electrical fields and to pH. In energized mitochondria the uptake of Tl⁺ would occur electrophoretically, while Tl⁺/H⁺ exchange would constitute a leak. In the presence of NO ₃ ^– , the movements of Tl⁺ are determined by that of NO ₃ ^– , indicating short-range coupling of electrical forces. At low concentrations of Tl⁺, 5 mM or less, there was no indication of a Tl⁺/H⁺ exchange, which appears to be induced by high concentrations of Tl⁺.     

Bivalent Metal Ions Modulate Cd2+ Effects on Isolated Rat Liver Mitochondria

We have studied Cd²⁺-induced effects on mitochondrial respiration and swelling in various media as a function of the [Cd²⁺] in the presence or absence of different bivalent metal ions or ruthenium red (RR). It was confirmed by monitoring oxygen consumption by isolated rat liver mitochondria that, beginning from 5 M, Cd²⁺ decreased both ADP and uncoupler-stimulated respiration and increased their basal respiration when succinate was used as respiratory substrate. At concentrations higher than 5 M, Cd²⁺ stimulated ion permeability of the inner mitochondrial membrane, which was monitored in this study by swelling of both nonenergized mitochondria in 125 mM KNO₃ or NH₄NO₃ medium and succinate-energized mitochondria incubated in a medium containing 25 mM K-acetate and 100 mM sucrose. We have found substantial changes in the above-mentioned Cd²⁺ effects on mitochondria treated in sequence with 100 M of Ca²⁺, Sr²⁺, Mn²⁺ or Ba²⁺(Me²⁺) and 7.5 M RR, as well as the alterations in Cd²⁺ action on the uptake of ¹³⁷Cs⁺ by succinate-energized mitochondria in the presence or absence of valinomycin in acetate medium (50 mM Tris-acetate and 140 mM sucrose) with or without Ca²⁺ or RR. The evidence obtained indicate that Ca²⁺ exhibits a synergestic action on all Cd²⁺ effects examined, whereas Sr²⁺ and Mn²⁺, conversely, are antagonistic. In the presence of RR, the Cd²⁺ effects on respiration [stimulation of State 4 respiration and inhibition of 2,4-dinitrophenol (DNP)-uncoupled respiration] still exist, but are observed at concentrations of cadmium more than one order higher; the inhibition of State 3 respiration by Cd²⁺, conversely, takes place under even lower cadmium concentrations than those determined without RR in the medium. In addition, RR added simultaneously with cadmium in the incubation medium prevents any swelling in the nitrate media, but induces an increment both in Cd²⁺-stimulated swelling and ¹³⁷Cs⁺ (analog of K⁺) uptake in the acetate media. For the first time, we have shown that Cd²⁺-induced swelling in all media under study is susceptible to cyclosporin A (CSA), a high-potency inhibitor of the mitochondrial permeability transition (PT) pore. The observations are interpreted in terms of a dual effect of cadmium on respiratory chain activity and permeability transition.     

Effect of oxidative processes in mitochondria on contractility of heart muscle of the frog <Emphasis Type="Italic">Rana temporaria</Emphasis>. Actions of Cd<Superscript>2+</Superscript>

The inotropic Cd²⁺ action on frog heart is studied with taking into account its toxic effects upon mitochondria. Cd²⁺ at concentrations of 1, 10, and 20 mM is established to decrease dose dependently (21.3, 50.3, and 72.0%, respectively) the muscle contraction amplitude; this is explained by its competitive action on the potential-controlled Na²⁺-channels of the L-type (Ca_v 1.2). In parallel experiments on isolated rat heart mitochondria (RHM) it was shown that Cd²⁺ at concentrations of 15 and 25 mM produces swelling of non-energized and energized mitochondria in isotonic (with KNO₂ and NH₂NO₃) and hypoosmotic (with 25 mM CH₃COOK) media. Study of oxidative processes in RHM by polarographic method has shown 20 mM Cd²⁺ to disturb activity of respiratory mitochondrial chain. The rate of endogenous respiration of isolated mitochondria in the medium with Cd²⁺ in the presence of malate and succinate was approximately 5 times lower than in control. In experimental preparations, addition into the medium of DNP—uncoupler of oxidation and phosphorylation did not cause an increase of the oxygen consumption rate. Thus, the obtained data indicate that a decrease in the cardiac muscle contractility caused by Cd²⁺ is due not only to its direct blocking action on Ca²⁺-channels, but also is mediated by toxic effect on rat heart mitochondria, which was manifested as an increase in ion permeability of the inner mitochondrial membrane (IMM), acceleration of the energy-dependent K⁺ transport into the matrix of mitochondria, and inhibition of their respiratory chain.     

Mitochondrial energetics, pH regulation, and ion dynamics: a computational-experimental approach

We developed a computational model of mitochondrial energetics that includes Ca²⁺, proton, Na⁺, and phosphate dynamics. The model accounts for distinct respiratory fluxes from substrates of complex I and complex II, pH effects on equilibrium constants and enzyme kinetics, and the acid-base equilibrium distributions of energy intermediaries. We experimentally determined NADH and ΔΨ_m in guinea pig mitochondria during transitions from de-energized to energized, or during state 2/4 to state 3 respiration, or into hypoxia and uncoupling, and compared the results with those obtained in model simulations. The model quantitatively reproduces the experimentally observed magnitude of ΔΨ_m, the range of NADH levels, respiratory fluxes, and respiratory control ratio upon transitions elicited by sequential additions of substrate and ADP. Simulation results are also able to mimic the change in ΔΨ_m upon addition of phosphate to state 4 mitochondria, leading to matrix acidification and ΔΨ_m polarization. The steady-state behavior of the integrated mitochondrial model qualitatively simulates the dependence of respiration on the proton motive force, and the expected flux-force relationships existing between respiratory and ATP synthesis fluxes versus redox and phosphorylation potentials. This upgraded mitochondrial model provides what we believe are new opportunities for simulating mitochondrial physiological behavior during dysfunctional states involving changes in pH and ion dynamics.     

Action of La3+ on the systems providing contractility of vertebrate myocardium

The inotropic action of La³⁺ on frog myocardium was studied with taking into account its effect on mitochondria of cardiomyocytes (CM). It has been established that in the range of studied concentrations (0.2–6.0 mM), La³⁺ decreases dose-dependently the force of cardiac contractions (by 3.3–92.2%). In parallel experiments on isolated rat heart mitochondria (RHM), La³⁺ at a concentration of 25 μM has been shown to cause swelling of non-energized and energized mitochondria incubated in isotonic medium with 125 mM NH₄NO₃ and in hypotonic medium with 25 mM CH₃COOK. The study of oxidative processes in mitochondria with aid of polarographic method of measurement of oxygen concentration has shown that La³⁺ at concentrations of 50 and 100 μM increases the oxygen consumption rate by mitochondria in the state 2. However, La³⁺ does not decrease the respiration rate of isolated mitochondria in the state 3, as this takes place in the case of use of Cd²⁺ or at the Ca²⁺-overloading of mitochondria. The rate of endogenous respiration of isolated mitochondria in the medium with La³⁺ was higher than in control, which suggests its effect on ion permeability of the inner membrane. The data obtained in this work indicate that the La³⁺-produced decrease of contractility of cardiac muscle is not only due to the direct blocking effect on the potential-controlled Ca²⁺-channels, but is also mediated by its unspecific action on the CM mitochondria. This action is manifested as an acceleration of the energy-dependent K⁺ transport in matrix and as an increase of ion permeability of the inner mitochondrial membrane (IMM).     

Mechanisms of antioxidant activities of quercetin and catechin

Abstract

The seleno-organic compound ebselen mimics the glutathione-dependent, hydroperoxide reducing activity of glutathione peroxidase. The activity of glutathione peroxidase determines the rate of hydroperoxide-induced Ca²⁺ release from mitochondria. Ebselen stimulates Ca²⁺ release from mitochondria, accelerates mitochondrial respiration and uncoupling, and induces mitochondrial swelling, indicating a deterioration of mitochondrial function. These manifestations are abolished by cyclo-sporine A, a potent inhibitor of the mitochondrial permeability transition. However, when ebselen-induced Ca²⁺ cycling is prevented with ruthenium red, an inhibitor of the Ca²⁺ uniporter, or by chelation of extramitochondrial Ca²⁺ by EGTA, no detectable elevation of swelling or uncoupling is observed. The release of Ca²⁺ from mitochondria is delayed in the absence of rotenone, i.e. when pyridine nucleotides are maintained in the reduced state due to succinate-driven reversed electron flow. We suggest that ebselen induces Ca²⁺ release from intact mitochondria via an NAD⁺ hydrolysis-dependent mechanism.     

Control of the pyridine nucleotide-linked Ca release from mitochondria by respiratory substrates

Oxidation of mitochondrial pyridine nucleotides followed by their hydrolysis promotes Ca²⁺ release from intact liver mitochondria. In most of the previous studies oxidation was achieved with pro-oxidants which were added to mitochondria respiring on succinate in the presence of rotenone, a site I-specific inhibitor of the respiratory chain. Here we investigate pro-oxidant dependent and independent Ca²⁺ release from mitochondria when respiration is supported either by the NAD⁺-linked substrate β-hydroxybutyrate, or by succinate. In the presence, as well as in the absence, of the pro-oxidant t-butylhydroperoxide mitochondria retain Ca²⁺ much better with succinate than with β-hydroxybutyrate, as respiratory substrate. When Ca²⁺ release is induced by t-butylhydroperoxide succinate-supported Ca²⁺ retention is impeded by rotenone. Ca²⁺ release (pro-oxidant dependent or independent) is paralleled by oxidation and hydrolysis of intramitochondrial pyridine nucleotides, and Ca²⁺ retention is paralleled by reduction of pyridine nucleotides. It is concluded that the pyridine nucleotide-linked Ca²⁺ release from mitochondria can be controlled by respiratory substrates which regulate the intramitochondrial hydrolysis of oxidized pyridine nucleotides.     

Duality of effect of La3+ on mitochondrial permeability transition pore depending on the concentration

In order to explore the role of mitochondria in proliferation promotion and/or apoptosis induction of lanthanum, the mutual influences between La³⁺ and Ca²⁺ on mitochondrial permeability transition pore (PTP) opening were investigated with isolated mitochondria from rat liver. The experimental results revealed that La³⁺ influence the state of mitochondria in a concentration-dependent biphasic manner. La³⁺ in nanomolar concentrations, acting as a Ca²⁺ analog, entered mitochondrial matrix via the RuR sensitive Ca²⁺ channel and elevated ROS level, leading to opening of PTP indicated by mitochondrial swelling, reduction of ΔΨ_m and cytochrome c release. Inhibition of PTP with 10 μM CsA attenuated the effects of La³⁺. However, micromolar concentrations La³⁺ acted mainly as a Ca²⁺ antagonist, inhibiting PTP opening induced by Ca²⁺. We postulated that this action of La³⁺ on mitochondria through interaction with Ca²⁺ might be involved in the proliferation-promoting and apoptosis induction by La³⁺.     

The interaction of La 3+ with mitochondria in relation to respiration-coupled Ca 2+ transport

La³⁺ inhibits the respiration-dependent accumulation of Ca²⁺ by rat liver mitochondria when added in very small amounts (0.1–l.0 nmole per mg protein). However, La³⁺ itself does not activate respiration. With the use of ¹⁴⁰La³⁺ it was found that La³⁺ is very rapidly bound to rat liver mitochondria in a respiration-independent process accompanied by loss of H⁺ to the medium. When both La³⁺ and Ca²⁺ are added to mitochondria simultaneously, most of the La³⁺ but little Ca²⁺ are bound. La³⁺ added to mitochondria previously loaded with Ca²⁺ is tightly bound without discharge of Ca²⁺. Conversely, when Ca²⁺ is added to La³⁺-loaded mitochondria it is not bound nor is the La³⁺ discharged. La³⁺ inhibits both high-affinity and low-affinity respiration-independent Ca²⁺ binding. Isotopic experiments showed that La³⁺ is, in fact, bound to the same high-affinity sites as Ca²⁺, in both intact mitochondria and in mitochondrial extracts. It is concluded (1) that La³⁺ binds to and inhibits the Ca²⁺ carrier; (2) that La³⁺ is not transported by the Ca²⁺ carrier; and (3) that La³⁺ is, in addition, bound to a large number of external sites on mitochondria for which Ca²⁺ is not a strong competitor.     

Mitochondrial Ca2+ transport and permeability transition pore opening and mitochondrial energetic status

The relationship between mitochondrial Ca²⁺ transport and permeability transition pore (PTP) opening as well as the effects of mitochondrial energetic status on mitochondrial Ca²⁺ transport and PTP opening were studied. The results showed that the calcium-induced calcium release from mitochondria (mCICR) induced PTP opening. Inhibitors for electron transport of respiratory chain inhibited mCICR and PTP opening. Partial recovery of electron transport in respiratory chain resulted in partial recovery of mCICR and PTP opening. mCICR and PTP opening were also inhibited by CCCP which eliminated transmembrane proton gradient. The results indicated that mitochondrial Ca²⁺ transport and PTP opening are largely dependent on electron transport and energy coupling.     

The effect of taurine on the ion transport system in mitochondria

The effect of taurine on the ATP-dependent mitochondrial swelling that characterizes the activity of mitochondrial ATP-dependent K⁺ channel and the formation of Ca²⁺-dependent pores, different in sensitivity to cyclosporin A, has been studied in rat liver mitochondria. It has been shown that taurine in micromolar concentrations (0.5–125 μM) stimulates the energy-dependent swelling of mitochondria. Taurine in physiological concentrations (0.5–20 mM) has no effect on the ATP-dependent swelling and the formation of cyclosporin A-insensitive Pal/Ca²⁺-activated pore in mitochondria. Taurine in these concentrations increased the rate of cyclosporin A-sensitive swelling of mitochondria induced by Ca²⁺ and P_i and reduced the Ca²⁺ capacity of mitochondria. The different effects of physiological taurine concentrations on the ATP-dependent transport of K⁺ and Ca²⁺ ions in mitochondrial membranes as compared with cell membranes are discussed.