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.     

Glycyrrhetinic acid as inhibitor or amplifier of permeability transition in rat heart mitochondria

Glycyrrhetinic acid (GE), a hydrolysis product of glycyrrhizic acid, one of the main constituents of licorice root, is able, depending on its concentration, to prevent or to induce the mitochondrial permeability transition (MPT) (a phenomenon related to oxidative stress) in rat heart mitochondria (RHM). In RHM, below a threshold concentration of 7.5 microM, GE prevents oxidative stress and MPT induced by supraphysiological Ca2+ concentrations. Above this concentration, GE induces oxidative stress by interacting with a Fe-S centre of Complex I, thus producing ROS, and amplifies the opening of the transition pore, once again induced by Ca2+. GE also inhibits Ca2+ transport in RHM, thereby preventing the oxidative stress induced by the cation. However, the reduced amount of Ca2+ transported in the matrix is sufficient to predispose adenine nucleotide translocase for pore opening. Comparisons between observed results and the effects of GE in rat liver mitochondria (RLM), in which the drug induces only MPT without exhibiting any protective effect, confirm that it interacts in a different way with RHM, suggesting tissue specificity for its action. The concentration dependence of the opposite effects of GE, in RHM but not RLM, is most probably due to the existence of a different, more complex, pathway by means of which GE reaches its target. It follows that high GE concentrations are necessary to stimulate the oxidative stress capable of inducing MPT, because of the above effect, which prevents the interaction of low concentrations of GE with the Fe-S centre. The reported results also explain the mechanism of apoptosis induction by GE in cardiomyocytes.     

Dependence of the inhibitory effect of metal cations on rat liver mitochondrial Ca2+ uptake on their physico-chemical properties

It has been found that Sr2+, La3+ Mn2+ (10-50 microM) inhibit Ca2+ transport into mitochondria in a competitive manner. Cd2+ ions show the mixed type inhibition of this transport. The inhibitory constants (Ki, microM) of the metals cations effect on Ca2+ transport increases in such a sequence: La3+ (2,11), Cd2+ (10,36), Mn2+ (49,29), Sr2+ (66,43). The metals cations inhibitory effect has an insignificant dependence on their ionic radii. But it is good correlated with the series of metals cations, based on the stability constants of their complexes with acetate (r = -0.96), aspartic (r = -0.91) and glutaminic acids and their hydratation enthalpy (r = -0.78). These data reveal that hydratation of metals cations and their interaction with carboxyles of Ca(2+)-uniporter plays an important role in the process of Ca2+ transport into mitochondrial matrix space and its inhibition by the metals cations. The mixed type inhibition of mitochondrial Ca2+ uptake by Cd2+ seems to be caused by the partial de-energization of mitochondria owing to Cd2+ interaction with SH-containing respiratory chain components and pore-forming ligands of mitochondrial membrane.     

Donepezil is a strong antagonist of voltage-gated calcium and potassium channels in molluscan neurons

Donepezil is an acetylcholinesterase inhibitor used in Alzheimer's disease therapy. The neuroprotective effect of donepezil has been demonstrated in a number of different models of neurodegeneration including beta-amyloid toxicity. Since the mechanisms of neurodegeneration involve the activation of both Ca(2+)- and K(+)-channels, the study of donepezil action on voltage-gated ionic currents looked advisable. In the present study, the action of donepezil on voltage-gated Ca(2+)- and K(+)-channels was investigated on isolated neurons of the edible snail (Helix pomatia) using the two-microelectrodes voltage-clamp technique. Donepezil rapidly and reversibly inhibited voltage activated Ca(2+)-current (I(Ca)) (IC(50)=7.9 microM) and three types of high threshold K(+)-current: Ca(2+)-dependent K(+)-current (I(C)) (IC(50)=6.4 microM), delayed rectifier K(+)-current (I(DR)) (IC(50)=8.0 microM) and fast transient K(+)-current (I(Adepol)) (IC(50)=9.1 microM). The drug caused a dual effect on low-threshold fast transient K(+)-current (I(A)), potentiating it at low (5 microM) concentration, but inhibiting at higher (7 microM and above) concentration. Donepezil also caused a significant hyperpolarizing shift of the voltage-current relationship of I(Ca) (but not of any type of K(+)-current). Results suggest the possible contribution of the blocking effect of donepezil on the voltage-gated Ca(2+)- and K(+)-channels to the neuroprotective effect of the drug.     

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).     

Properties of a new calcium ion antagonist on cellular uptake and mitochondrial efflux of calcium ions.

Compound YS 035 [NN-bis-(3,4-dimethoxyphenethyl)-N-methylamine] is a new synthetic compound capable of inhibiting Ca2+ uptake by different cells. The inhibition of Ca2+ uptake by muscle cells isolated from chicken embryo is dose-dependent in the compound YS 035 concentration range 10-30 microM. The new compound also inhibits Ca2+ entry into rat brain synaptosomes and less effectively into baby-hamster kidney cells. Compound YS 035 partially inhibits the slow Ca2+ release induced by Ruthenium Red and the rapid Na+-dependent efflux from heart mitochondria. The inhibition of the Na+/Ca2+ exchange appears to be of a non-competitive type with an apparent Ki of 28 microM. The new Ca2+ antagonist totally inhibits the Ca2+ efflux from liver mitochondria induced by Ruthenium Red, but it does not affect the release induced by uncoupler, respiratory inhibitor or chelator, nor the mitochondrial ATP synthesis and membrane potential. The properties shown by the new compound indicate it to be a Ca2+ antagonist and a useful tool for studies on the mitochondrial Ca2+ transport.     

Mechanism of vascular relaxation by thaligrisine: functional and binding assays

In the present study we examine the mechanism by which thaligrisine, a bisbenzyltetrahydroisoquinoline alkaloid, inhibits the contractile response of vascular smooth muscle. The work includes functional studies on rat isolated aorta and tail artery precontracted with noradrenaline or KCl. In other experiments rat aorta was precontracted by caffeine in the presence or absence of extracellular Ca2+. In order to assess whether thaligrisine interacts directly with calcium channel binding sites or with alpha-adrenoceptors we examined the effect of the alkaloid on [3H]-(+)-cis diltiazem, [3H]-nitrendipine and [3H]-prazosin binding to cerebral cortical membranes. The functional studies showed that the alkaloid inhibited in a concentration-dependent manner the contractile response induced by depolarization in rat aorta (IC50 = 8.9+/-2.9 microM, n=5) and in tail artery (IC50 = 3.04+/-0.3 microM, n=6) or noradrenaline induced contraction in rat aorta (IC50 = 23.0+/-0.39 microM, n=9) and in tail artery (IC50 = 3.8+/-0.9 microM, n=7). In rat aorta, thaligrisine concentration-dependently inhibited noradrenaline-induced contraction in Ca2+-free solution (IC50 = 13.3 microM, n=18). The alkaloid also relaxed the spontaneous contractile response elicited by extracellular calcium after depletion of noradrenaline-sensitive intracellular stores (IC50 = 7.7 microM, n=4). The radioligand receptor-binding study showed that thaligrisine has higher affinity for [3H]-prazosin than for [3H]-(+)-cis-diltiazem binding sites, with Ki values of 0.048+/-0.007 microM and 1.5+/-1.1 microM respectively. [3H]-nitrendipine binding was not affected by thaligrisine. The present work provides evidence that thaligrisine shows higher affinity for [3H]-prazosin binding site than [3H]-(+)-cis-diltiazem binding sites, in contrast with tetrandrine and isotetrandrine that present similar affinity for both receptors. In functional studies thaligrisine, acted as an alpha1-adrenoceptor antagonist and as a Ca2+ channel blocker, relaxing noradrenaline or KCl-induced contractions in vascular smooth muscle. This compound specifically inhibits the refilling of internal Ca2+-stores sensitive to noradrenaline, by blocking Ca2+-entry through voltage-dependent Ca2+-channels.     

A Specific Transduction Mechanism for the Glutamate Action on Phosphoinositide Metabolism via the Quisqualate Metabotropic Receptor in Rat Brain Synaptoneurosomes: II. Calcium Dependency, Cadmium Inhibition

In this article, we demonstrate that an increase in intracellular Ca2+ concentration may represent a specific common step(s) in the mechanism(s) of action of glutamate (Glu) and depolarizing agents on formation of inositol phosphates (IPs) in 8-day-old rat forebrain synaptoneurosomes. In fact, A23187, a Ca2+ ionophore, induces a dose-dependent accumulation of IPs, which is not additive with that evoked by Glu and K+ but is slightly synergistic with that induced by carbachol. In addition, Glu and K+ augment the intracellular Ca2+ concentration in synaptoneurosome preparations as measured by the fura-2 assay. The absence of external Ca2+ decreases basal and Glu-, and K(+)-stimulated formation of IPs. Cd2+ (100 microM) fully inhibits both Glu- and K(+)-evoked formation of IPs without affecting the carbachol-elicited response of IPs. Zn2+ inhibits Glu- and K(+)-stimulated accumulation of IPs (IC50 approximately 0.4 mM) but with a lower affinity than Cd2+ (IC50 approximately 0.035 mM). The organic Ca2+ channel blockers verapamil (10 microM), nifedipine (10 microM), omega-conotoxin (2 microM), and amiloride (10 microM) as well as the inorganic blockers Co2+ (100 microM) and La3+ (100 microM) block neither Glu- nor K(+)-evoked formation of IPs, a result suggesting that the opening of the L-, T-, N-, or P-type Ca2+ channels does not participate in these responses. All these data suggest that an increase in intracellular Ca2+ concentration resulting from an influx of Ca2+, sensitive to Cd2+ but not to other classical Ca2+ antagonists, may play a key role in the transduction mechanism activated by Glu or depolarizing agents.     

Why is inorganic phosphate necessary for uncoupling of oxidative phosphorylation by Cd2+ in rat liver mitochondria?

The phosphate (Pi)-dependent uncoupling action of Cd2+ in oxidative phosphorylation in rat liver mitochondria was studied mainly in terms of Pi transport. Cd2+ at 2 microM caused full uncoupling in the presence of 10 mM Pi, but no uncoupling in the absence of Pi. Cd2+ released state 4 respiration after a certain lag-time, and then the respiration increased progressively with time. After its addition, Cd2+ was taken up by mitochondria in a similar period to the lag time before respiratory release. KIH-201, a potent and specific inhibitor of Pi transport via the Pi/H+ symporter, abolished the uncoupling completely. Cd2+ caused dissipation of the electric transmembrane potential (delta psi) and swelling of mitochondria in a Pi-dependent manner. Uncoupling by Cd2+ was found to take place in parallel with the uptake of Pi into mitochondria via the Pi/H+ symporter, suggesting that the uncoupling was due to acceleration of H+ influx through the Pi/H+ symporter activated by Cd2+.     

Pathways of cadmium influx in mammalian neurons

The influx of the toxic cation Cd2+ was studied in fura 2-loaded rat cerebellar granule neurons. In cells depolarized with Ca2(+)-free, high-KCI solutions, the fluorescence emission ratio (R) increased in the presence of 100 microM Cd2(+). This increase was fully reversed by the Cd2+ chelator tetrakis(2-pyridylmethyl)ethylenediamine, indicating a cadmium influx into the cell. The rate of increase, dR/dt, was greatly reduced (67+/-5%) by 1 microM nimodipine and enhanced by 1 microM Bay K 8644. Concurrent application of nimodipine and omega-agatoxin IVA (200 nM) blocked Cd2+ permeation almost completely (88+/-5%), whereas omega-conotoxin MVIIC (2 microM) reduced dR/dt by 24+/-8%. These results indicate a primary role of voltage-dependent calcium channels in Cd2+ permeation. Stimulation with glutamate or NMDA and glycine also caused a rise of R in external Cd2+. Simultaneous application of nimodipine and omega-agatoxin IVA moderately reduced dR/dt (25+/-3%). NMDA-driven Cd2(+) entry was almost completely prevented by 1 mM Mg2+, 50 microM memantine, and 10 microM 5,7-dichlorokynurenic acid, suggesting a major contribution of NMDA-gated channels in glutamate-stimulated Cd2+ influx. Moreover, perfusion with alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate caused a slow increase of R. These results suggest that Cd2+ permeates the cell membrane mainly through the same pathways of Ca2+ influx.     

Positive heterotropic allosteric regulators of dihydropyridine binding increase the Ca2+ affinity of the L-type Ca2+ channel. Stereoselective reversal by the novel Ca2+ antagonist BM 20.1140.

The alpha 1-subunit of the voltage-dependent L-type Ca2+ channel has distinct, allosterically coupled binding domains for drugs from different chemical classes (dihydropyridines, benzothiazepines, phenylalkylamines, diphenylbutylpiperidines). (-)-BM 20.1140 (ethyl-2,2-di-phenyl-4-(1-pyrrolidino)-5-(2-picolyl)- oxyvalerate) is a novel Ca2+ channel blocker which potently stimulates dihydropyridine binding (K0.5 = 2.98 nM) to brain membranes. This property is shared by (+)-cis-diltiazem, (+)-tetrandrine, fostedil and trans-diclofurime, but (-)-BM 20.1140 does not bind in a competitive manner to the sites labeled by (+)-cis-[3H]diltiazem. (+)-cis-Diltiazem and (-)-BM 20.1140 have differential effects on the rate constants of dihydropyridine binding. (+)-BM 20.1140 reverses the stimulation of the positive allosteric regulators (pA2 value for reversal of (-)-BM 20.1140 stimulation = 7.4, slope 0.72). The underlying molecular mechanism of the potentiation of dihydropyridine binding has been clarified. The K0.5 for free Ca2+ to stabilize a high affinity binding domain for dihydropyridines on purified L-type channels from rabbit skeletal muscle is 300 nM. (+)-Tetrandine (10 microM) increases the affinity 8-fold (K0.5 for free Ca2+ = 30.1 nM) and (+)-BM 20.114 (10 microM) inhibits the affinity increase (K0.5 for free Ca2+ = 251 nM). Similar results were obtained with membrane-bound Ca(2+)-channels from brain tissue which have higher affinity for free Ca2+ (K0.5 for free Ca2+ = 132 nM) and for dihydropyridines compared with skeletal muscle. It is postulated that the dihydropyridine and Ca(2+)-binding sites are interdependent on the alpha 1-subunit, that the different positive heterotropic allosteric regulators (by their differential effects on Ca2+ rate constants) optimize coordination for Ca2+ in the channel pore and, in turn, increase affinity for the dihydropyridines.     

Intramitochondrial K+ as activator of carboxyatractyloside-induced Ca2+ release.

The role of intramitochondrial K+ content on the increase in membrane permeability to Ca2+, as induced by carboxyatractyloside was studied. In mitochondria containing a high K+ concentration (83 nmol/mg), carboxyatractyloside induced a fast and extensive mitochondrial Ca2+ release, membrane de-energization, and swelling. Conversely, in K(+)-depleted mitochondria (11 nmol/mg), carboxyatractyloside was ineffective. The addition of 40 mM K+ to K(+)-depleted mitochondria restored the capability of atractyloside to induce an increase in membrane permeability to Ca2+ release. The determination of matrix free Ca2+ concentration showed that, at an external free-Ca2+ concentration of 0.8 microM, control mitochondria contained 3.9 microM of free Ca2+ whereas K(+)-depleted mitochondria contained 0.9 microM free Ca2+. It is proposed that intramitochondrial K+ affects the matrix free Ca2+ concentration required to induce a state of high membrane permeability.     

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

The influence of mitochondrial ATP-dependent K(+)-channel (K+(ATP)-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 Ca(2+)-cycling supported by the simultaneous functioning of K(+)-channels and K+/H(+)-antiporter, and also Ca(2+)-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.     

Calcium transport and proton electrochemical potential gradient in mitochondria from guinea-pig cerebral cortex and rat heart

A method is described for the preparation of ;free' and ;synaptosomal' brain mitochondria from fractions of guinea-pig cerebral cortex respectively depleted and enriched in synaptosomes. Both preparations of mitochondria have a low membrane H(+) conductance, a high capacity to phosphorylate ADP, and a capacity to accumulate Ca(2+) at rates limited by the activity of the respiratory chain. Ca(2+) transport by ;free' brain mitochondria is compared with that of heart mitochondria. The Ca(2+) conductance of ;free' brain mitochondria was at least 20 times that for rat heart mitochondria. Ca(2+) uptake by brain mitochondria increased the pH gradient and decreased membrane potential, whereas little change occurred during the much slower uptake by heart mitochondria. In the presence of ionophore A23187, dissipative Ca(2+) cycling decreased the H(+) electrochemical potential gradient of brain mitochondria from 190 to 60mV, but caused only a slight decrease with heart mitochondria, although the ionophore lowered the pH gradient and increased membrane potential. The Ca(2+) conductance of ;free' brain mitochondria is distinctive in showing a hyperbolic dependency on free Ca(2+) concentration. In the presence of Ruthenium Red, a rapid Na(+)-dependent Ca(2+) efflux occurs. The H(+) electrochemical potential gradient is maintained during this efflux, and membrane potential increases, with both ;free' brain and heart mitochondria. The Na(+) requirement for Ca(2+) efflux appears not to be related to the high Na(+)/H(+) exchange activity but may represent a direct exchange of Na(+) for Ca(2+).     

Contribution of ATP synthase to stimulation of respiration by Ca2+ in heart mitochondria

A variety of experimental conditions were applied with the aim to estimate the correlation between the contribution of ATP synthase to the respiratory flux control and the calcium-induced activation of succinate oxidation in heart mitochondria isolated from rat, rabbit and guinea pig. The sensitivity of respiration in heart mitochondria to the decrease in temperature from 37 degrees C to 28 degrees C decreases in the order rabbit > guinea pig > rat. Ca2+ effect on succinate oxidation rate in state 3 respiration was species- and temperature-dependent and ranged from 0 (rat, 37 degrees C) to +44% (rabbit, 28 degrees C). For mitochondria from all experimental animals, the increase of Ca2+ in physiological range of concentration did not change state 2 respiration rate, and the stimulatory effect of Ca2+ on state 3 respiration was more pronounced at 28 degrees C than at 37 degrees C. The respiratory subsystem was sensitive to Ca2+ ions only in rabbit heart mitochondria. A high positive correlation between Ca2+ ability to stimulate succinate oxidation in state 3 and the control exerted by ATP synthase over the respiratory flux provides argument confirming stimulation of ATP synthase by Ca2+ ions.     

Effect of Sodium Ions on Calcium-Loaded Rat Heart Mitochondria and Frog Myocardium

Journal of Evolutionary Biochemistry and Physiology - The effect of calcium load on rat heart mitochondria [RHM(K+)], in which K+ ions in the matrix were partially replaced by Na+ ions [RHM(Na+)],...     

Protective role of chlorpromazine on lead-induced damage to heart mitochondria.

1. The protective effect of chlorpromazine (CPZ) on the toxic effects of lead in mitochondrial functions was studied. 2. The findings indicate that CPZ at a concentration of 50 microM protects heart mitochondria against lead-induced Ca2+ uptake inhibition. 3. In addition, CPZ inhibits the drop of the transmembrane potential, as well as mitochondrial swelling as induced by 10 microM Pb2+. 4. It is proposed that the protective effect of chlorpromazine can be due to its stabilizing action on biological membranes.     

Oxidation of mitochondrial pyridine nucleotides by aglycone derivatives of adriamycin.

Adriamycin (AdM) and related anthracyclines are potent antineoplastic agents, the clinical utility of which is limited by severe cardiotoxicity. Aglycone derivatives of AdM have recently been reported to trigger the release of Ca2+ from isolated, preloaded rat heart mitochondria and to modify mitochondrial sulfhydryl (-SH) groups. Both mitochondrial Ca2+ retention and -SH status are sensitive to mitochondrial NAD(P)+/NAD(P)H ratios. This investigation examined the effects of AdM and its aglycone derivatives on the pyridine nucleotide redox status of isolated, intact heart mitochondria with the following results. (i) AdM aglycones induced the slow, Ca2(+)-independent oxidation of mitochondrial NAD(P)H. Oxidation was proportional to aglycone concentration between 5 and 60 microM. (ii) In terms of potency, 7-deoxy AdM aglycone greater than or equal to 7-hydroxy AdM aglycone much greater than AdM. (iii) Inhibitor data suggested that NAD(P)H oxidation reflects the rotenone-insensitive reduction of AdM aglycone and subsequent electron transfer to O2 generating superoxide. (iv) NAD(P)H oxidation mediated by AdM aglycone could be distinguished from the Ca2(+)-dependent NAD(P)H oxidation associated with mitochondrial Ca2+ release. This communication is the first to describe redox interactions of AdM with intact mitochondria.     

Synergistic deleterious effect of micromolar Ca ions and free radicals on respiratory function of heart mitochondria at cytochrome C and its salvage trial

Both Ca2+ and free radicals (FR) are accumulated in temporarily ischemic myocardium and might cause reperfusion injury. Respiratory function measured by polarography of isolated heart mitochondria before or after the in vitro treatment with Ca2+ (1.2 microM) and/or FR showed that Ca2+ or FR per se showed no or weak effect on state 3, but cotreatment of Ca2+ and FR prominently deteriorated state 3, state 4 and RCI. The injury was speculated to occur at cytochrome c itself or its reductase from enzyme assay in the respiratory chain. Furthermore, contrary to the published data, the synergistic action was not mitigated by phospholipase A2 inhibitors (dibucaine, mepacrine), membrane stabilizers (lidocaine, coenzyme Q10), Ca entry blocker (verapamil) or superoxide dismutase, suggesting refractory to therapy.     

In vivo studies on the toxic effects of microcystins on mitochondrial electron transport chain and ion regulation in liver and heart of rabbit

This study examined the toxic effects of microcystins on mitochondria of liver and heart of rabbit in vivo. Rabbits were injected i.p. with extracted microcystins (mainly MC-RR and -LR) at two doses, 12.5 and 50 MC-LReq. microg/kg bw, and the changes in mitochondria of liver and heart were studied at 1, 3, 12, 24 and 48 h after injection. MCs induced damage of mitochondrial morphology and lipid peroxidation in both liver and heart. MCs influenced respiratory activity through inhibiting NADH dehydrogenase and enhancing succinate dehydrogenase (SDH). MCs altered Na(+)-K(+)-ATPase and Ca(2+)-Mg(2+)-ATPase activities of mitochondria and consequently disrupted ionic homeostasis, which might be partly responsible for the loss of mitochondrial membrane potential (MMP). MCs were highly toxic to mitochondria with more serious damage in liver than in heart. Damage of mitochondria showed reduction at 48 h in the low dose group, suggesting that the low dose of MCs might have stimulated a compensatory response in the rabbits.