Isolation of highly coupled heart mitochondria in high yield using a bacterial collagenase

Hyperoxemic reperfusion after prolonged cardiac arrest in a rat cardiopulmonary bypass resuscitation model

BACKGROUND

The effect of hyperoxygenation at reperfusion, particularly in the setting of cardiac arrest, remains unclear. This issue was studied in a prolonged cardiac arrest model consisting of 25 min cardiac arrest in a rat resuscitated with cardiopulmonary bypass (CPB). The objective of this study was to determine the effect of hyperoxygenation following prolonged cardiac arrest resuscitation on mitochondrial and cardiac function.

METHODS

Male Sprague-Dawley rats (400-450 g) were anesthetized with ketamine and xylazine and instrumented for closed chest cardiopulmonary bypass (CPB). Following a 25-min KCl-induced cardiac arrest, the animals were resuscitated by CPB with 100% oxygen. Three minutes after successful return of spontaneous circulation (ROSC), the animals received either normoxemic reperfusion (CPB with 40-50% oxygen) or hyperoxemic reperfusion (CPB with 100% oxygen) for 1 h. Post-resuscitation hemodynamics, cardiac function, mitochondrial function and immunostaining of 3-nitrotyrosine were compared between the two different treatment groups.

RESULTS

At 1 h after ROSC, the hyperoxemic reperfusion group had a significant higher mean arterial pressure, less metabolic acidosis and better diastolic function than the normoxemic reperfusion group. Cardiac mitochondria from the hyperoxemic reperfusion group had a higher respiratory control ratio (RCR) and cardiac tissue showed less nitroxidative stress compared to the normoxemic reperfusion group.

CONCLUSIONS

One hour of hyperoxemic reperfusion after 25 min of cardiac arrest in an in vivo CPB model resulted in significant short-term improvement in myocardial and mitochondrial function compared with 1h of normoxemic reperfusion. This myocardial response may differ from previously reported post-arrest hyperoxia mediated effects following shorter arrest times.

Inhibition of cytochrome c release by 10-N-nonyl acridine orange, a cardiolipin-specific dye, during myocardial ischemia-reperfusion in the rat

The release of cytochrome c from the mitochondria to the cytosol is a critical step for downstream caspase-mediated apoptotic signal transduction in ischemia-reperfusion (I/R)-induced myocardial tissue injury. 10-N-nonyl acridine orange (NAO), a cardiolipin-specific dye, has been shown to inhibit Bid-mediated cytochrome c release from isolated mitochondria in vitro; however, the possible protective effects of NAO and the mechanisms underlying the protection from myocardial I/R-induced tissue injury in a rat model are unknown. Male Sprague-Dawley rats were subjected to a 30-min coronary arterial occlusion followed by reperfusion. All rats received either vehicle or NAO (100 microg/kg iv) 10 min before the occlusion. The infarct size in the heart at 24 h after reperfusion was significantly reduced in NAO-treated rats compared with vehicle-treated rats. NAO treatment significantly reduced the cytosolic cytochrome c contents and caspase-9 activity in the ischemic region but did not affect caspase-8 activity. Furthermore, NAO treatment markedly suppressed the translocation of truncated Bid, a proapoptotic Bcl-2 family member, to the mitochondrial fraction. NAO also suppressed the mitochondrial swelling and oxygen uptake stimulated by calcium overload. The results suggest that NAO possesses protective effects against myocardial I/R injury, which may be due to the suppression of cytochrome c release through blockade of truncated Bid translocation to mitochondria and inhibition of the opening of mitochondrial permeability transition pores.

Mitochondrial generation of reactive oxygen species is enhanced at the Q(o) site of the complex III in the myocardium of Trypanosoma cruzi-infected mice: beneficial effects of an antioxidant

In this study, we have characterized the cellular source and mechanism for the enhanced generation of reactive oxygen species (ROS) in the myocardium during Trypanosoma cruzi infection. Cardiac mitochondria of infected mice, as compared to normal controls, exhibited 63.3% and 30.8% increase in ROS-specific fluorescence of dihydroethidium (detects O(2) (*-)) and amplex red (detects H(2)O(2)), respectively. This increase in ROS level in cardiac mitochondria of infected mice was associated with a 59% and 114% increase in the rate of glutamate/malate- (complex I substrates) and succinate- (complex II substrate) supported ROS release, respectively, and up to a 74.9% increase in the rate of electron leakage from the respiratory chain when compared to normal controls. Inhibition studies with normal cardiac mitochondria showed that rotenone induced ROS generation at the Q(Nf)-ubisemiquinone site in complex I. In complex III, myxothiazol induced ROS generation from a site located at the Q(o) center that was different from the Q(i) center of O(2) (*-) generation by antimycin. In cardiac mitochondria of infected mice, the rate of electron leakage at complex I during forward (complex I-to-complex III) and reverse (complex II-to-complex I) electron flow was not enhanced, and complex I was not the main site of increased ROS production in infected myocardium. Instead, defects of complex III proximal to the Q(o) site resulted in enhanced electron leakage and ROS formation in cardiac mitochondria of infected mice. Treatment of infected mice with phenyl-alpha-tert-butyl-nitrone (PBN) improved the respiratory chain function, and, subsequently, decreased the extent of electron leakage and ROS release. In conclusion, we show that impairment of the Q(o) site of complex III resulted in increased electron leakage and O(2) (*-) formation in infected myocardium, and was controlled by PBN.

Cardiac mitochondria in heart failure: decrease in respirasomes and oxidative phosphorylation

Aims

Mitochondrial dysfunction is a major factor in heart failure (HF). A pronounced variability of mitochondrial electron transport chain (ETC) defects is reported to occur in severe acquired cardiomyopathies without a consistent trend for depressed activity or expression. The aim of this study was to define the defect in the integrative function of cardiac mitochondria in coronary microembolization-induced HF.

Methods and results

Studies were performed in the canine coronary microembolization-induced HF model of moderate severity. Oxidative phosphorylation was assessed as the integrative function of mitochondria, using a comprehensive variety of substrates in order to investigate mitochondrial membrane transport, dehydrogenase activity and electron-transport coupled to ATP synthesis. The supramolecular organization of the mitochondrial ETC also was investigated by native gel electrophoresis. We found a dramatic decrease in ADP-stimulated respiration that was not relieved by an uncoupler. Moreover, the ADP/O ratio was normal, indicating no defect in the phosphorylation apparatus. The data point to a defect in oxidative phosphorylation within the ETC. However, the individual activities of ETC complexes were normal. The amount of the supercomplex consisting of complex I/complex III dimer/complex IV, the major form of respirasome considered essential for oxidative phosphorylation, was decreased.

Conclusions

We propose that the mitochondrial defect lies in the supermolecular assembly rather than in the individual components of the ETC.

Myoglobin-enhanced oxygen delivery to isolated cardiac mitochondria

The heart, red skeletal muscles and the nitrogen-fixing legume root nodule function in steady states of high oxygen influx, partial oxygenation of cytoplasmic myoglobin or leghemoglobin and correspondingly low oxygen partial pressure. Here, we ask: what conditions are required at the surface of actively respiring, state III, tightly coupled mitochondria to enhance oxygen flow to cytochrome oxidase? Pigeon heart mitochondria were isolated with minimal damage to the outer mitochondrial membrane and were incubated at low oxygen pressures, where respiration is oxygen limited, with solutions of each of six monomeric hemoglobins with widely divergent kinetics and equilibria in their reactions with oxygen: Busycon myoglobin, horse myoglobin, Lucina hemoglobins I and II, soybean leghemoglobin c and Gasterophilus hemoglobin. Each augments oxygen uptake. The declining fractional saturation of each hemoglobin with oxygen was monitored spectrophotometrically as mitochondrial respiration depleted the oxygen; the oxygen partial pressure at half-maximal rate of oxygen uptake was similar for each hemoglobin, supporting the conclusion that the hemoglobins did not interact with the mitochondrial surface in oxygen delivery. The oxygen pressure required to support state III mitochondrial oxygen uptake, 0.005 kPa (0.04 torr), is small compared with that obtained in the sarcoplasm and at the mitochondrial surface of the working heart, 0.32 kPa (2.4 torr). We conclude that, in normal steady states of contraction of the myoglobin-containing heart, oxygen utilization by mitochondrial cytochrome oxidase is not limited by oxygen availability.

A possible site of superoxide generation in the complex I segment of rat heart mitochondria

We searched for possible sites of superoxide generation in the complex I segment of the respiratory chain by studying both forward and reverse electron transfer reactions in isolated rat heart mitochondria. Superoxide production was monitored by measuring the release of hydrogen peroxide from mitochondria with a fluorescence spectrophotometer using the Amplex red/horseradish peroxidase system. In the forward electron transfer, a slow superoxide production in the presence of glutamate and malate was enhanced by both rotenone and piericidin A (specific inhibitors at the end of the complex I respiratory chain). Both diphenileneiodonium and ethoxyformic anhydride (inhibitors for respiratory components located upstream of the respiratory chain) inhibited the enhancement by rotenone and piericidin A. In contrast, in reverse electron transfer driven by ATP, both diphenileneiodonium and ethoxyformic anhydride enhanced the superoxide production. Piericidin A also increased superoxide production. Rotenone increased it only in the presence of piericidin A. Our results suggest that the major site of superoxide generation is not flavin, but protein-associated ubisemiquinones which are spin-coupled with iron-sulfur cluster N2.

Functional disorders of the oxidative phosphorylation system in the heart mitochondria of mice with juvenile visceral steatosis

Mice with juvenile visceral steatosis (JVS) develop remarkable cardiac hypertrophy and exhibit an increased number of mitochondria in their heart. However, the biochemical characteristics and physiological functions of these mitochondria cardiac are little known. Here we show that the respiratory activities at state 3 with glutamate plus malate or succinate in the heart mitochondria of JVS mice were greatly decreased to 47% or 77%, respectively, compared with those of control mice. The contents of cytochromes a+a(3), b, and c+c(1) in the heart mitochondria of these mice were also decreased, to 51%, 45%, and 79%, respectively, of those of the control mice. Oligomycin-sensitive ATPase activitiy in these mitochondria, however, was increased to about 2 times over that of the control mice. Surprisingly, the ATP-Pi exchange activity of the heart mitochondria of JVS mice was greatly decreased, to 35% of that of control mice. On the other hand, the expression levels of 2 subunits of H(+)-ATP synthase, i.e., coupling factor 6 and alpha subunit, in heart mitochondria from control and JVS mice were almost the same. These results indicate that the coordinate regulation of mitochondrial proliferation and gene expression for components of the oxidative phosphorylation system was markedly defective in the heart of JVS mice. Our current results also suggest the presence of a novel regulatory mechanisms of ATP synthase activities in the heart.

Changes of carp FoF1-ATPase in association with temperature acclimation

Previously we have shown, using two-dimensional electrophoresis, that mitochondrial ATP synthase (F(o)F(1)-ATPase) beta-subunit is the 55-kDa protein increased in cold-acclimated carp Cyprinus carpio (Kikuchi K, Itoi S, and Watabe S. Fisheries Sci 65: 629-636, 1999). To clarify the coordinate expression in various subunits of carp F(o)F(1)-ATPase with temperature acclimation, we examined the differences in mRNA levels of mitochondrial proteins encoded by both nuclear and mitochondrial genes in fast muscle of carp acclimated to 10 and 30 degrees C. The mRNA levels of nuclear genes per unit weight of total RNA were nearly twofold higher in the 10 degrees C- than 30 degrees C-acclimated carp. However, the transcripts of mitochondrial genes for the 10 degrees C-acclimated carp in terms of the same comparing unit were six to seven times as much as those for the 30 degrees C-acclimated carp. The F(o)F(1)-ATPase activities measured at 10, 25, and 30 degrees C were nearly twofold higher for the cold-acclimated fish than their warm-acclimated counterparts. Such quantitative and qualitative changes in carp F(o)F(1)-ATPase may contribute to extra ATP production required to compensate for energy balance at suboptimal temperatures.

Sulfide oxidation coupled to ATP synthesis in chicken liver mitochondria

Chicken liver mitochondria consumed O2 at an accelerated rate when supplied with low concentrations of hydrogen sulfide. Maximum respiration occurred in 10 microM sulfide, and continued more slowly up to concentrations as high as 60 microM. Sulfide oxidation was coupled to adenosine triphosphate (ATP) synthesis, as shown by firefly luciferase luminescence and by measurement of the mitochondrial membrane electrochemical gradient. Synthesis of ATP required low, steady-state concentrations of sulfide (< 5 microM), which were maintained by use of a syringe pump. The ratio of consumed O2 to sulfide changed at low sulfide and O2 concentrations, indicating alternative metabolic reactions and products. In low concentrations of sulfide, presumably most similar to physiological, the O2/sulfide ratio was 0.75. This is the first report of sulfide oxidation linked to ATP synthesis in any organism not specifically adapted to a sulfide-rich environment. We suggest that this may be a widespread mitochondrial trait, and that it is consistent with the hypothesis that mitochondria originated from sulfide-oxidizing symbionts.

Identification of respiratory complexes I and III as mitochondrial sites of damage following exposure to ionizing radiation and nitric oxide

In 32D cl 3 hematopoietic progenitor cells, the overexpression of manganese superoxide dismutase (MnSOD, SOD2), the enzyme normally found in mitochondria, protects against the damaging effects of ionizing radiation. In the presence of a nitric oxide donor, which exacerbates the damage, inhibition of mitochondrial function can be demonstrated to be associated with respiratory complexes I (NADH dehydrogenase) and III (cytochrome c reductase), but not II (succinate dehydrogenase), IV (cytochrome c oxidase), or V (ATP synthase). The same pattern of inhibition is observed in the case of isolated bovine heart mitochondria exposed to ionizing radiation and the nitric oxide donor. The addition of authentic peroxynitrite (ONO2(-)) to isolated mitochondria also results in damage to complexes I and III (but not II, IV, and V), as shown by assays of electron-transfer activities and electron paramagnetic resonance (EPR) spectroscopic measurements, suggesting ONO2(-) to be responsible for most of the observed radiation damage in both the cultured cell lines and isolated mitochondria. It is argued that, in general, production of ONO2(-) is an important contributor to radiation damage in biological systems and the implications of these findings in relation to possible mechanisms of oxidant-linked apoptosis are briefly considered.

Cardiolipins and mitochondrial proton-selective leakage

The proton-selective leak (State 4 respiratory rate) but not delta psi, in mitochondria from thyroid-sensitive tissues, responds to in vivo stimuli in unique correlation with changes in cardiolipins, saturated and mono-unsaturated (extended) fatty acyl contents, cardiolipins/phospholipids ratios, and/or membrane outer-sidedness. Liver mitochondrial State 4 respiration, basal in fasted rats, contributes little to resting metabolic rate in fed rats, where State 3 depresses delta psi. In a proposed model, an essential inner-membrane outer-surface proton antenna collects protons and donates them, via a water-shuttle, to transmembrane porters: transient water-molecule-chains between extended phospholipid acyls; protonophores, and uncoupling proteins. Only cardiolipin microdomains can donate, from an anomalously-dissociating phosphate group in each headgroup; unadapted cardiolipins have few conducting water chains. Thyroid states regulate each cardiolipin property, and are permissive, via the proton antenna, for proton leaks, including those through adapted and possibly constitutive BAT and ectopic uncoupling proteins. Slow leakage in liposomes may reflect insufficient cardiolipin proton antennas.

Optimization of preparation of mitochondria from 25-100 mg skeletal muscle

A method for isolation of mitochondria from 25-100 mg skeletal muscle is described. The instrumental developments include a refined homogenization setup, special handling techniques, and equipment for biopsy storage. The preparation medium was a standard ionic medium. All fractions were assayed for marker enzymes and the data used in optimization of the yield. It was observed that the homogenization procedure exerts strong control on the integrity of the isolated mitochondria. The method was developed with pigeon breast muscle as the model tissue and used virtually unaltered for preparation from muscles of pigs, rats, and humans. The relative yield was 40-50% and the mitochondria were well coupled and showed high rates of phosphorylating respiration.

Structural features of a multisubstate cardiac mitoplast anion channel: inferences from single channel recording

Ion channels from sheep cardiac mitoplast (inverted inner mitochondrial membrane vesicle) preparations were incorporated into voltage-clamped planar lipid bilayers. A low-conductance anion channel (approximately 40 or approximately 85 pS in symmetric 300 or 550 mM choline Cl, respectively), characterized by the presence of two well-defined substates, at approximately 25 and approximately 50% of the fully open level, was studied in detail. The substate behavior was consistent with a multibarelled channel containing four functionally coupled pores. At negative (cis-trans) membrane potentials, the putative protomers appeared to gate with substantial positive cooperativity, accounting for the apparent absence of a approximately 75% sublevel. At positive holding potentials, allosteric promoter interactions were more complicated, and the channel complex could be modeled as a dimer of dimers. The protochannels in one dimer ("dimer A") appeared to open independently of each other, and with a relatively high probability, while the monomers comprising the second dimer ("dimer B") were functionally coupled, could only open if both protomers in dimer A were open, and closed as soon as one of the monomers in dimer A shut. The channels also displayed Ca(2+)-(and Mg(2+)-) sensitive rectification related to bilayer lipid surface charge. By assuming that Ca2+ acted solely by screening surface charge, the membrane surface potential profile was used as a "microscopic ruler" to place one month of the channel within 10-11 A of the bilayer surface.

Single anion channels reconstituted from cardiac mitoplasts

Ion channels from sheep cardiac mitoplast (inverted inner mitochondrial membrane vesicle) preparations were incorporated into voltage-clamped planar lipid bilayers. The appearance of anion rather than cation channels could be promoted by exposing the bilayers to osmotic gradients formed by Cl- salts of large, relatively impermeant, cations at a pH of 8.8. Two distinct activities were identified. These comprised a multisubstate anion channel of intermediate conductance (approximately 60 pS in 300 vs. 50 mM choline Cl, approximately 100 pS in symmetric 150 mM KCl), and a lower-conductance anion channel (approximately 25 or approximately 50 pS in similar conditions), which only displayed two well-defined substates, at approximately 25 and approximately 50% of the fully open state. The larger channels were not simple multiples of the lower-conductance channels, but both discriminated poorly, and to a similar extent, between anions and cations (PCl-/Pcholine+ approximately 12, PCl-/PK+ approximately 8). The lower-conductance channel was only minimally selective between different anions (PNO3-(1.0) = PCl- > PBr- > PI- > PSCN-(0.8)), and its conductance failed to saturate even in high (> 1.0 M) activities of KCl. The channels were not obviously voltage dependent, and they were unaffected by 0.5 mM SITS, H2O2, propranolol, quinine or amitriptyline, or by 2 mM ATP, or by variations in pH (5.5-8.8). Ca2+ and Mg2+ did not alter single channel activity, but did modify single current amplitudes in the lower-conductance channel. This effect, together with voltage-dependent substate behavior, is described in the following paper.

Carnitine palmitoyltransferase in the heart is controlled by a different mechanism than the hepatic enzyme

Diminished sensitivity of hepatic carnitine palmitoyltransferase to inhibition by malonyl-CoA in the fasting and diabetic states is a well-recognized aspect of the regulatory mechanism for hepatic fatty acid oxidation. Inhibition of myocardial carnitine palmitoyltransferase by malonyl-CoA may play an important role in regulation of fatty acid oxidation in the heart, but there has been a discrepancy in data relating to changes in malonyl-CoA sensitivity of the myocardial carnitine palmitoyltransferase during fasting. Analysis of malonyl-CoA inhibition of myocardial carnitine palmitoyltransferase in fasting and fed states under a variety of conditions has indicated that under no condition could any difference be found in malonyl-CoA sensitivity that was attributable to fasting. Proteolysis of the outer carnitine palmitoyltransferase led to artifactual changes in sensitivity due to the appearance of partial inhibition. We have concluded that the sensitivity of myocardial carnitine palmitoyltransferase to malonyl-CoA does not change during fasting. Changes in fatty acid oxidation in the heart are probably due to changes in malonyl-CoA concentrations or to other inhibitors.

Cardiolipins and biomembrane function

Evidence is discussed for roles of cardiolipins in oxidative phosphorylation mechanisms that regulate State 4 respiration by returning ejected protons across and over bacterial and mitochondrial membrane phospholipids, and that regulate State 3 respiration through the relative contributions of proteins that transport protons, electrons and/or metabolites. The barrier properties of phospholipid bilayers support and regulate the slow proton leak that is the basis for State 4 respiration. Proton permeability is in the range 10(-3)-10(-4) cm s-1 in mitochondria and in protein-free membranes formed from extracted mitochondrial phospholipids or from stable synthetic phosphatidylcholines or phosphatidylethanolamines. The roles of cardiolipins in proton conductance in model phospholipid membrane systems need to be assessed in view of new findings by Hübner et al. [313]: saturated cardiolipins form bilayers whilst natural highly unsaturated cardiolipins form nonlamellar phases. Mitochondrial cardiolipins apparently participate in bilayers formed by phosphatidylcholines and phosphatidylethanolamines. It is not yet clear if cardiolipins themselves conduct protons back across the membrane according to their degree of fatty acyl saturation, and/or modulate proton conductance by phosphatidylcholines and phosphatidylethanolamines. Mitochondrial cardiolipins, especially those with high 18:2 acyl contents, strongly bind many carrier and enzyme proteins that are involved in oxidative phosphorylation, some of which contribute to regulation of State 3 respiration. The role of cardiolipins in biomembrane protein function has been examined by measuring retained phospholipids and phospholipid binding in purified proteins, and by reconstituting delipidated proteins. The reconstitution criterion for the significance of cardiolipin-protein interactions has been catalytical activity; proton-pumping and multiprotein interactions have yet to be correlated. Some proteins, e.g., cytochrome c oxidase are catalytically active when dimyristoylphosphatidylcholine replaces retained cardiolipins. Cardiolipin-protein interactions orient membrane proteins, matrix proteins, and on the outerface receptors, enzymes, and some leader peptides for import; activate enzymes or keep them inactive unless the inner membrane is disrupted; and modulate formation of nonbilayer HII-phases. The capacity of the proton-exchanging uncoupling protein to accelerate thermogenic respiration in brown adipose tissue mitochondria of cold-adapted animals is not apparently affected by the increased cardiolipin unsaturation; this protein seems to take over the protonophoric role of cardiolipins in other mitochondria. Many in vivo influences that affect proton leakage and carrier rates selectively alter cardiolipins in amount per mitochondrial phospholipids, in fatty acyl composition and perhaps in sidedness; other mitochondrial membrane phospholipids respond less or not at all.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of etomoxiryl-CoA on different carnitine acyltransferases

The effects of etomoxiryl-CoA on purified carnitine acyltransferases and on carnitine acyl-transferases of rat heart mitochondria and rat liver microsomes were determined. At nanomolar concentrations, the data agreed with that of other investigators who have shown that etomoxiryl-CoA must be binding to a high affinity site with specific inhibition of mitochondrial carnitine palmitoyltransferase (CPTo). Micromolar amounts of etomoxiryl-CoA inhibited both short- and long-chain carnitine acyltransferases. The concentrations of etomoxiryl-CoA required for 50% inhibition of the different carnitine acetyltransferases and microsomal and peroxisomal carnitine octanoyltransferase were in the low micromolar range. Mixed-type and uncompetitive inhibition kinetics were obtained, depending on the source of purified enzyme. When purified rat heart CPT was incubated with etomoxiryl-CoA, it increased the K0.5 and decreased the Hill coefficient for acyl-CoA. Both proteins and phospholipids of mitochondria and microsomes formed covalent adducts of [3H]etomoxir, with the predominant labeling in phospholipids. None of the purified enzymes formed covalent adducts when incubated with [3H]etomoxiryl-CoA, in contrast to intact mitochondria or microsomes. The major 3H-labeled protein for rat heart mitochondria had a molecular weight of 81,000 +/- 4000, and the major proteins from microsomes had a molecular weight of 51,000-57,000. Malonyl-CoA prevented most of the tritum incorporation into the 81,000 Da protein of mitochondria, but it had little effect on incorporation of tritiated etomoxir into the 51,000-57,000 Da proteins of microsomes. When 50 microM etomoxiryl-CoA was added to microsomes and to mitochondria that had been incubated with radioactive etomoxiryl-CoA, much of the radioactive etomoxir disappeared from the major microsomal proteins, but virtually none was displaced from the mitochondrial protein. Thus, at least two different types of covalent etomoxir complexes were formed. This pulse-chase experiment showed that the mitochondrial protein-etomoxir complex was not turned over, consistent with other data showing that etomoxir inhibited carnitine palmitoyltransferase. In contrast, the major protein-etomoxir complex in microsomes was turned over during the pulse-chase experiment.

Transport of cyanide into guinea pig cardiac mitochondria

The transport of cyanide (CN) into cells has been presumed to be by passive diffusion. Recently, there have been reports that CN, in the form of an anion, may enter the cell by active or facilitated transport. To characterize the mechanism(s) and kinetics of CN movement across the cell membrane, we measured the rate of 14CN (Na salt) uptake into guinea-pig mitochondria. Initial velocities of CN movement into mitochondria were determined at time points ranging from 10-100 msec and at CN concentrations ranging from 1 microM-10 mM using a rapid filtration device. A Hofstee plot of the data suggests that an active or facilitated transport predominates at lower CN concentrations (less than 10 microM), whereas passive diffusion of CN predominates at higher CN concentrations. The kinetic constants for the active phase transport were Jmax = 0.9 pmol/ms and Kt = 14 microM. These results suggest that a large portion of CN movement across the cell membrane is due to an active or facilitated transport phenomenon.

The effect of inorganic phosphate on chick (Gallus domesticus) heart mitochondrial volume and cation content

1. In the absence of exogenous Ca(II), Pi induces a swelling change that is kinetically first order with k = 1.08 +/- 0.1 min-1. The first-order rate constant is independent of [Pi] over the range of 0.5-45 mM. 2. In the presence of exogenous substrate, the volume change induced by Pi is monophasic and can be reversed by ADP. 3. The swelling process and the approach to steady state is accompanied by controlled losses of both K+ and Mg(II) from within the mitochondria. 4. The loss of K+ is biphasic as a function of time with ki = 14.1 +/- 1.6 and k2 = 4.4 +/- 0.34 nmol min-1 mg mitochondria-1. 5. The loss of Mg(II) is monophasic and the rate at which this cation is released decreases as a function of time. Ca(II) fluxes are not involved in the volume occurring secondary to Pi uptake. 6. In the absence of exogenous substrate, Pi induces a triphasic change in mitochondrial volume. 7. The sequence of volume changes corresponds to an initial first-order swelling secondary to the addition of Pi, a contraction apparently triggered by the loss of approximately 85% of total intra-mitochondrial Mg(II), and a second larger swelling phase that cannot be reversed with ADP. 8. The Pi-induced swelling of chick heart mitochondria is not inhibited by EGTA and does not depend on the provision of exogenous Ca(II). 9. The Ca(II) and Mg(II) ions released from within the mitochondria are responsible for activating divalent cation-dependent ATPases which cosediment with isolated chick heart mitochondria.

Further investigation on the high-conductance ion channel of the inner membrane of mitochondria

By use of the patch-clamp technique, the inner membrane of mouse liver and heart mitochondria is shown to contain a highly conductive (around 100 pS in symmetrical 150 mM KCl) and voltage-dependent ion channel. This channel closely resembles that previously found in cuprizone-treated mouse liver inner mitochondrial membrane. The paper discusses the electrical properties of the channel and its possible physiological function. The reconstitution in giant liposomes of a partially purified ox heart inner membrane fraction containing the channel and the use of various inhibitors are also presented.

Cytochrome c oxidase deficiency in subacute necrotizing encephalopathy (Leigh syndrome)

Tissues and cultured fibroblasts from two patients with Leigh syndrome (subacute necrotizing encephalopathy) were examined. A systemic defect in cytochrome oxidase was identified by enzyme assay and estimation of cytochrome concentrations. Immunochemical analysis showed a reduction of most subunits of the cytochrome oxidase complex. The rate of synthesis of cytochrome oxidase subunits, determined by labelling experiments in cultured fibroblasts, was the same in the patients and normal controls. The reduced cytochrome oxidase content of the patients' tissues must therefore result from abnormal turnover of the protein subunits.

Effect of malonyl-CoA on the kinetics and substrate cooperativity of membrane-bound carnitine palmitoyltransferase of rat heart mitochondria

The effect of malonyl-CoA on the kinetic parameters of carnitine palmitoyltransferase (outer) the outer form of carnitine palmitoyltransferase (palmitoyl-CoA: L-carnitine O-palmitoyltransferase, EC 2.3.1.21) from rat heart mitochondria was investigated using a kinetic analyzer in the absence of bovine serum albumin with non-swelling conditions and decanoyl-CoA as the cosubstrate. The K0.5 for decanoyl-CoA is 3 microM for heart mitochondria from both fed and fasted rats. Membrane-bound carnitine palmitoyltransferase (outer) shows substrate cooperativity for both carnitine and acyl-CoA, similar to that exhibited by the enzyme purified from bovine heart mitochondria. The Hill coefficient for decanoyl-CoA varied from 1.5 to 2.0, depending on the method of assay and the preparation of mitochondria. Malonyl-CoA increased the K0.5 for decanoyl-CoA with no apparent increase in sigmoidicity or Vmax. With 20 microM malonyl-CoA and a Hill coefficient of n = 2.1, the K0.5 for decanoyl-CoA increased to 185 microM. Carnitine palmitoyltransferase (outer) from fed rats had an apparent Ki for malonyl-CoA of 0.3 microM, while that from 48-h-fasted rats was 2.5 microM. The kinetics with L-carnitine were variable: for different preparations of mitochondria, the K0.5 ranged from 0.2 to 0.7 mM and the Hill coefficient varied from 1.2 to 1.8. When an isotope forward assay was used to determine the effect of malonyl-CoA on carnitine palmitoyltransferase (outer) activity of heart mitochondria from fed and fasted animals, the difference was much less than that obtained using a continuous rate assay. Carnitine palmitoyltransferase (outer) was less sensitive to malonyl-CoA at low compared to high carnitine concentrations, particularly with mitochondria from fasted animals. The data show that carnitine palmitoyltransferase (outer) exhibits substrate cooperativity for both acyl-CoA and L-carnitine in its native state. The data show that membrane-bound carnitine palmitoyltransferase (outer) like carnitine palmitoyltransferase purified from heart mitochondria exhibits substrate cooperativity indicative of allosteric enzymes and indicate that malonyl-CoA acts like a negative allosteric modifier by shifting the acyl-CoA saturation to the right. A slow form of membrane-bound carnitine palmitoyltransferase (outer) was not detected, and thus, like purified carnitine palmitoyltransferase, substrate-induced hysteretic behavior is not the cause of the positive substrate cooperativity.

In vivo and in vitro effects of aluminum treatment on rat liver mitochondrial function

This study examines the effect on mitochondrial respiration and permeability of in vivo and in vitro aluminium (Al) exposure. Rats were treated intraperitoneally with AlCl3 to achieve serum and liver Al concentrations comparable to those seen in Al-related disorders. Mitochondria isolated from Al-treated rats had higher (p<0.01) Al concentration, lower (p<0.05) state 3 respiration, respiratory control (RCR), and ADP/O ratio (succinate substrate), and greater passive swelling in 100 mM KCl or 200 mM NH4NO3 than controls. The in vitro addition of Al (0-180 μM) to mitochondria from normal rats also decreased (p<0.01) state 3 respiration, RCR, and ADP/O and stimulated passive swelling in KCl and NH4NO3 at 42-180 μM Al. These studies show that Al depresses mitochondrial energy metabolism and increases membrane permeability. The toxicity associated with Al may be related to its effect on mitochondria.