Stabilising action of carnitine on energy linked processes in rat liver mitochondria

Hypoxia-induced lipid peroxidation in the brain during postnatal ontogenesis

Reactive oxygen species (ROS) are common products of the physiological metabolic reactions, which are associated with cell signaling and with the pathogenesis of various nervous disorders. The brain tissue has the high rate of oxidative metabolic activity, high concentration of polyunsaturated fatty acids in membrane lipids, presence of iron ions and low capacity of antioxidant enzymes, which makes the brain very susceptible to ROS action and lipid peroxidation formation. Membranes of brain cortex show a higher production of thiobarbituric acid-reactive substances (TBARS) in prooxidant system (ADP.Fe(3+)/NADPH) than membranes from the heart or kidney. Lipid peroxidation influences numerous cellular functions through membrane-bound receptors or enzymes. The rate of brain cortex Na(+),K(+)-ATPase inhibition correlates well with the increase of TBARS or conjugated dienes and with changes of membrane fluidity. The experimental model of short-term hypoxia (simulating an altitude of 9000 m for 30 min) shows remarkable increase in TBARS in four different parts of the rat brain (cortex, subcortical structures, cerebellum and medulla oblongata) during the postnatal development of Wistar rat of both sexes. Young rats and males are more sensitive to oxygen changes than adult rats and females, respectively. Under normoxia or hypobaric hypoxia both ontogenetic aspects and sex differences play a major role in establishing the activity of erythrocyte catalase, which is an important part of the antioxidant defense of the organism. Rats pretreated with L-carnitine (and its derivatives) have lower TBARS levels after the exposure to hypobaric hypoxia. The protective effect of L-carnitine is comparable with the effect of tocopherol, well-known reactive species scavenger. Moreover, the plasma lactate increases after a short-term hypobaric hypoxia and decreases in L-carnitine pretreated rats. Acute hypobaric hypoxia and/or L-carnitine-pretreatment modify serum but not brain lactate dehydrogenase activity. The obtained data seem to be important because the variations in oxygen tension represent specific signals of regulating the activity of many specific systems in the organism.

Acetyl-L-carnitine suppresses thyroid hormone-induced and spontaneous anuran tadpole tail shortening

Mitochondrial membrane permeability transition (MPT) plays a crucial role in apoptotic tail shortening during anuran metamorphosis. L-carnitine is known to shuttle free fatty acids (FFAs) from the cytosol into mitochondria matrix for β-oxidation and energy production, and in a previous study we found that treatment with L-carnitine suppresses 3, 3', 5-triiodothyronine (T3 ) and FFA-induced MPT by reducing the level of FFAs. In the present study we focus on acetyl-L-carnitine, which is also involved in fatty acid oxidation, to determine its effect on T3 -induced tail regression in Rana rugosa tadpoles and spontaneous tail regression in Xenopus laevis tadpoles. The ladder-like DNA profile and increases in caspase-3 and caspase-9 indicative of apoptosis in the tails of T3 -treated tadpoles were found to be suppressed by the addition of acetyl-L-carnitine. Likewise, acetyl-L-carnitine was found to inhibit thyroid hormone regulated spontaneous metamorphosis in X. laevis tadpoles, accompanied by decreases in caspase and phospholipase A2 activity, as well as non-ladder-like DNA profiles. These findings support our previous conclusion that elevated levels of FFAs initiate MPT and activate the signaling pathway controlling apoptotic cell death in tadpole tails during anuran metamorphosis.

A Bax/Bak-independent Mechanism of Cytochrome c Release

Bax and Bak are multidomain pro-apoptotic members of the Bcl-2 family of proteins that regulate mitochondria-mediated apoptosis by direct modulation of mitochondrial membrane permeability. Since double-knock-out mouse embryonic fibroblasts with deficiency of Bax and Bak are resistant to multiple apoptotic stimuli, Bax and Bak are considered to be an essential gateway for various apoptotic signals. Here we showed that the combination of calcium ionophore A23187 and arachidonic acid induced cytochrome c release and caspase-dependent death of double-knock-out mouse embryonic fibroblasts, indicating that other mechanisms of cytochrome c release exist. Furthermore, A23187/arachidonic acid (ArA)-induced caspase-dependent death was significantly suppressed by the treatment of several serine protease inhibitors including 4-(2-aminoethyl)benzenesulfonylfluoride and l-1-chloro-3-(4-tosylamido)-4-phenyl-2-butanone but not the overexpression of anti-apoptotic Bcl-2 family of proteins or the inhibition of mitochondrial membrane permeability transition. These results indicate that there are at least two mechanisms of cytochrome c release leading to caspase activation, a Bax/Bak-dependent mechanism and a Bax/Bak-independent, but serine protease(s)-dependent, mechanism.

Activity of lactate dehydrogenase in serum and cerebral cortex of immature and mature rats after hypobaric hypoxia

In our previous studies we have found both an increase of lipid peroxidation damage (expressed as levels of thiobarbituric acid-reactive substances) in brain and plasma lactate concentration in 21-day-old rats after a 30-min exposure to hypobaric hypoxia. Pretreatment of rats with L-carnitine decreased both parameters. The aim of our present study was to determine if the L-carnitine-dependent decrease of plasma lactate could be due to a modification of lactate dehydrogenase (LDH) activity. We followed brain and blood serum LDH activity of 14-, 21- and 90-day-old Wistar rats. We found an increase of brain LDH activity with age. However, we did not observe any significant differences in LDH activity after exposure to hypobaric hypoxia or L-carnitine pretreatment. In contrast to brain, serum LDH activity did not show any clear age-dependence. The hypoxia exposure increased LDH activity of 21-day-old rats only. Pretreatment of rats with L-carnitine decreased serum LDH activity of 21- and 90-day-old rats probably due to membrane stabilizing role of L-carnitine. In conclusions, acute hypobaric hypoxia and/or L-carnitine pretreatment modified serum but not brain LDH activity.

Bioenergetic approaches for neuroprotection in Parkinson's disease

There is considerable evidence suggesting that mitochondrial dysfunction and oxidative damage may play a role in the pathogenesis of Parkinson's disease (PD). This possibility has been strengthened by recent studies in animal models, which have shown that a selective inhibitor of complex I of the electron transport gene can produce an animal model that closely mimics both the biochemical and histopathological findings of PD. Several agents are available that can modulate cellular energy metabolism and that may exert antioxidative effects. There is substantial evidence that mitochondria are a major source of free radicals within the cell. These appear to be produced at both the iron-sulfur clusters of complex I as well as the ubiquinone site. Agents that have shown to be beneficial in animal models of PD include creatine, coenzyme Q(10), Ginkgo biloba, nicotinamide, and acetyl-L-carnitine. Creatine has been shown to be effective in several animal models of neurodegenerative diseases and currently is being evaluated in early stage trials in PD. Similarly, coenzyme Q(10) is also effective in animal models and has shown promising effects both in clinical trials of PD as well as in clinical trials in Huntington's disease and Friedreich's ataxia. Many other agents show good human tolerability. These agents therefore are promising candidates for further study as neuroprotective agents in PD.

Roles of long chain fatty acids and carnitine in mitochondrial membrane permeability transition

Palmitoyl-CoA (Pal-CoA) lowered the respiratory control ratio (RCR), and induced mitochondrial membrane permeability transition (MPT) and cytochrome c (Cyt. c) release from isolated rat liver mitochondria. L-Carnitine suppressed the Pal-CoA-induced dysfunction, MPT, and Cyt. c release of isolated mitochondria. This suppression was inhibited by cephaloridine, an inhibitor of carnitine uptake into mitochondria. Cyclosporin A (CsA), an inhibitor of MPT, and BSA also suppressed the Pal-CoA-induced MPT. In the presence of inorganic phosphate (P(i)), Ca2+-induced MPT was suppressed by BSA, L-carnitine, and chlorpromazine, an inhibitor of phospholipase A2. In the presence of a low concentration of Ca2+, 3,3',5-triiodothyronine, long chain fatty acids, salicylic acid, and diclofenac induced MPT by a mechanism that was suppressed by BSA, L-carnitine, or chlorpromazine. During the incubation of mitochondria on ice, their respiratory competence decreased; L-carnitine and BSA also prevented this decrease. Mitochondrial depolarization in pheochromocytoma PC12 cells was induced by either serum deprivation or arachidonic acid by a mechanism that was suppressed by acetyl-L-carnitine. These results indicate that some MPTs may be regulated by fatty acid metabolism and that the Pal-CoA-induced MPT plays an important role in the induction of apoptosis.

The action of acetyl-L-carnitine on the neurotoxicity evoked by amyloid fragments and peroxide on primary rat cortical neurones

The amyloid beta-peptides have been implicated in the excitotoxic mechanism of neuronal injury in the pathogenesis of Alzheimer's disease. In this paper we examine the effect of different amyloid fragments (beta A1-40, A1-28, and A25-35), as well as potential neuroprotective compounds on rat cortical neuron viability. Exposure of neurones to beta A25-35 or A1-40 at concentrations as low as 1 microgram/ml inhibited, significantly, the MTT response and this level of inhibition was similar after 24-h or three-day exposure. Furthermore, the level of inhibition was not affected by the presence or absence of 5% horse serum in the medium. Preexposure (10 min) of neurones to ALC at concentrations of 0.1, 1, 5, and 10 mM attenuated the inhibition of the MTT response caused by beta A25-35 (50 micrograms/ml) in serum free medium for 24 h. The treatment of cells with vitamin E (100 microM), catalase (4 mg/ml), NGF (0.1 and 10 ng/ml), or cycloheximide (0.1 microgram/ml) significantly restored the MTT response that was inhibited by beta A25-35. The mechanism for the protective actions of these compounds against beta A25-35 toxicity is not clear but may involve free radical scavenger action and preservation of energy production, although other mechanisms, especially for ALC, such as a direct effect on A-beta interaction with charged anionic phospholipids and/or stabilizing action on membranes, are also possible.

The effects of the ergosteroid 7-oxo-dehydroepiandrosterone on mitochondrial membrane potential: possible relationship to thermogenesis

Administered 3 beta-hydroxyandrost-5-ene-7,17-dione (7-oxo-DHEA) is more effective than 3 beta-hydroxyandrost-5-en-7-one (DHEA) as an inducer of liver mitochondrial sn-glycerol-3-phosphate dehydrogenase and cytosolic malic enzyme in rats. Like DHEA, the 7-oxo metabolite enhances liver catalase, fatty acylCoA oxidase, cytosolic sn-glycerol-3-phosphate dehydrogenase, mitochondrial substrate oxidation rate, and the reconstructed sn-glycerol 3-phosphate shuttle. The mitochondrial adenine nucleotide carrier is diminished by thyroidectomy and is restored to normal activity by administering 7-oxo-DHEA. The relationship between respiratory rate and proton motive force across the mitochondrial membrane was measured in the nonphosphorylating state. When treated with increasing concentrations of respiratory inhibitors liver mitochondria from rats treated with 7-oxo-DHEA or thyroid hormones show a more rapid decline of membrane potential than do normal liver mitochondria. Thus 7-oxo-DHEA induces an increased proton leak or slip as has been reported for the thyroid hormone by M.D. Brand [(1990) Biochem. Biophys. Acta 1018, 128-133]. This process may contribute to the enhanced thermogenesis caused by ergosteroids as well as by thyroid hormones.

Protective actions of L-carnitine and acetyl-L-carnitine on the neurotoxicity evoked by mitochondrial uncoupling or inhibitors

The mechanism for the pathological increase in cell death in various disease states e.g. HIV immunodefficiency or even ageing or Alzheimer's disease, occurs by complex and as yet undefined mechanism(s) related to immunological, virological or biochemical disturbances (i.e. energy depletion, oxidative stress, increased protein degradation). We have studied mitochondrial uncoupling or inhibitor toxicity on neurones at the cellular level and at the mitochondrial level using rhodamine (Rh123) and 10-nonylacridine orange (NAO) fluorescence with confocal microscopy. Blockade of the mitochondrial chain complexes at various points was studied. The possible protective effects of the compound L-carnitine, which plays a central role in mitochondrial function, was tested in this form of neurotoxicity. It appears that L-carnitine and its acetylated form, acetyl-L-carnitine, can attenuate the cell damage, as assessed by lactate dehydrogenase (LDH) release, evoked by the uncoupler, p-(trifluoromethoxy)phenylhdyrazone (FCCP), or by the inhibitors, 3-nitropropionic acid (3-NPA) or rotenone. Further, the FCCP-induced inhibition of Rh123 uptake was antagonized by the preincubation of cells with L-carnitine. Since such neurotoxic mechanisms may be operating in the various pathological forms of myotoxicity and neurotoxicity, these observations suggest potential for a therapeutic approach.

L-carnitine and some of its analogs delay the onset of apoptotic cell death initiated in murine C2.8 hepatocytic cells after hepatocyte growth factor deprivation

Addition of L-carnitine and some of its analogs to low-serum incubation medium of murine hepatocytic C2.8 cells prolonged maintenance of life and enhanced cell growth, as compared to controls. The drug acted synergistically with hepatocyte growth factor (HGF). Addition of L-carnitine to cells that had grown confluently in medium supplemented with HGF, significantly delayed the onset of cell death (apoptosis) initiated after HGF deprivation. Protection by L-carnitine was dose-dependent and stereospecific. Similar findings were obtained with three analogs of L-carnitine (i.e. isovaleryl-L-carnitine-HCl, isovaleryl-L-carnitine acid fumarate and butyryl L-carnitine taurine amide). In contrast, four different analogs (i.e. isovaleryl-L-carnitine-eptyl-ester-HCl, isovaleryl-L-carnitine-idroxy-butyric-HCl, L-threonyl-L-carnitine-HCl and L-paramethyl-cinnamoil-carnitine-HCl) were inactive. Although the mechanism of cytoprotection stimulated by L-carnitine remains unresolved, the data suggest that this compound serves as a co-factor that influences C2.8 cells to become less susceptible to damaging actions of noxious agents or conditions initiated after HGF withdrawal.

Tissue lipid accumulation by L-aminocarnitine, an inhibitor of carnitine-palmitoyltransferase-2. Studies in intact rats and isolated mitochondria

Tissues of fasted animals treated with L-aminocarnitine (L-3-amino-4-trimethylaminobutyrate) showed an accumulation of long-chain acylcarnitines and triacylglycerols. Blood levels of free fatty acids, long-chain acylcarnitines and triacylglycerol-rich lipoproteins were found to be increased, whereas glucose was reduced. The liver mitochondria isolated from rats treated with L-aminocarnitine utilized both pyruvate and succinate normally, but were not able to oxidize palmitoylcarnitine. In vitro oxidation of palmitoylcarnitine by liver mitochondria was inhibited by L-aminocarnitine in a concentration-dependent fashion in contrast to succinate and pyruvate oxidation which was not modified. L-aminocarnitine proved to be a potent and selective inhibitor (IC50 = 805 nM) of the carnitine palmitoyltransferase isoenzyme, located on the inner side of the mitochondrial inner membrane (CPT2). The activity of the carnitine palmitoyltransferase isoenzyme located on the mitochondrial outer membrane inhibitable by malonyl-CoA (IC50 = 19 microM), was not inhibited by 0.8 microM L-aminocarnitine. Both in vitro and in vivo effects of L-aminocarnitine suggest that the substance has a specific and potent inhibitory action on CPT2. Its in vivo inhibition results in a dramatic increase of long-chain acylcarnitines in various organs, that it is why this increase can be considered a very good marker of CPT2 inhibition. A markedly altered lipid metabolism was observed.

Mechanisms by which mitochondria transport calcium

It has been firmly established that the rapid uptake of Ca2+ by mitochondria from a wide range of sources is mediated by a uniporter which permits transport of the ion down its electrochemical gradient. Several mechanisms of Ca2+ efflux from mitochondria have also been extensively discussed in the literature. Energized mitochondria must expend a significant amount of energy to transport Ca2+ against its electrochemical gradient from the matrix space to the external space. Two separate mechanisms have been found to mediate this outward transport: a Ca2+/nNa+ exchanger and a Na(+)-independent efflux mechanism. These efflux mechanisms are considered from the perspective of available energy. In addition, a reversible Ca2(+)-induced increase in inner membrane permeability can also occur. The induction of this permeability transition is characterized by swelling of the mitochondria, leakiness to small ions such as K+, Mg2+, and Ca2+, and loss of the mitochondrial membrane potential. It has been suggested that the permeability transition and its reversal may also function as a mitochondrial Ca2+ efflux mechanism under some conditions. The characteristics of each of these mechanisms are discussed, as well as their possible physiological functions.

L-carnitine delays the killing of cultured hepatocytes by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

The role of fatty acid metabolism in chemical-dependent cell injury is poorly understood. Addition of L-carnitine to the incubation medium of cultured hepatocytes delayed cell killing initiated by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Protection by L-carnitine was stereospecific and observed as late as 1 h following addition of MPTP. D-Carnitine, but not iodoacetate, reversed the L-carnitine effect. Monoamine oxidase A and B activities, MPTP/N-methyl-4-phenyl-pyridinium levels, and MPTP-dependent loss of mitochondrial membrane potential measured by release of [3H]triphenylmethylphosphonium were not altered by addition of L-carnitine. Significant changes in MPTP-induced depletion of total cellular ATP did not occur with excess L-carnitine. Although the mechanism of cytoprotection exerted by L-carnitine remains unresolved, the data suggest that L-carnitine does not significantly alter: (i) mitochondrial-dependent bioactivation of MPTP; (ii) MPTP-dependent loss of mitochondrial membrane potential; or (iii) MPTP-mediated depletion of total cellular ATP content. We conclude that alterations of fatty acid metabolism may contribute to the toxic consequences of exposure to MPTP. Moreover, the lack of L-carnitine-mediated cytoprotection of monolayers incubated with 4-phenylpyridine or potassium cyanide suggests: (i) a link between fatty acid metabolism and mitochondrial membrane-mediated, bioactivation-dependent cell killing; and (ii) that inhibition of NADH dehydrogenase may not totally explain the mechanism of MPTP cytotoxicity.

Carnitine: metabolism and clinical chemistry

In man carnitine is synthesized from proteic trimethyllysine in liver, brain and kidney. Muscles which contain approximately 98% of carnitine must take it up from the blood in an exchange process with endogenous deoxycarnitine, the immediate precursor of carnitine. Uneven organ distribution of the enzymes catalyzing carnitine synthesis further implies an inter-organ transport of the intermediates. Assay of these intermediates in blood may assist causal definition of carnitine deficiency syndromes. Besides catalyzing the transport of long-chain acyls in mitochondria, carnitine is necessary for the export of intra-mitochondrially produced short-chain acyls and for trapping and elimination of unphysiological acyls (benzoic, pivalic, valproic acids etc.). Unlike the corresponding acyl-CoA, carnitine esters are capable of diffusing across cellular membranes, and may be eliminated in urine, distributed in tissues or both. Assay of physiological and unphysiological carnitine esters in urine is necessary for the diagnosis of carnitine insufficiencies.

Ca2+-mediated action of long-chain acyl-CoA on liver mitochondria energy-linked processes

The decrease of steady-state transmembrane potential (delta psi) and loss of accumulated Ca2+ are magnified if palmitoyl-CoA is added to rat liver mitochondria exposed to Ca2+ and phosphate. The extent of this damage increases with increasing concentration of long-chain acyl-CoA. Addition of L-carnitine with or without the addition of palmitoyl-CoA considerably delays the deenergization. In the latter case, there is a substantial decrease in the assayed endogenous long-chain acyl-CoA content. This protective action of L-carnitine is abolished by L-aminocarnitine, a powerful inhibitor of carnitine palmitoyl transferase (palmitoyl-CoA: L-carnitine O-palmitoyltransferase, EC 2.3.1.21.). The removal of Ca2+ by EGTA, or the inhibition of its uptake by Ruthenium red or Mg2+ further enhances the degree of protection.

Protection against acute hyperammonemia: the role of quaternary amines

The quaternary amine L-carnitine is able to protect Swiss Albino mice from hyperammonemia when administered in high doses before ammonium acetate. This has been explained by its specific ability to shuttle fatty acids into mitochondria. The structure of L-carnitine resembles the chemical structure of other substances that have been described as being able to protect living cells against osmotic stress. We subjected Swiss Albino mice to hyperammonemia after pretreatment with L-carnitine or "osmoprotectants" such as the quaternary amines choline and betaine, and trimethylamine N-oxide. L-Carnitine proved to be the drug of choice to protect against acute hyperammonemia. Nevertheless, the other tested compounds appeared also to be effective, suggesting that osmoregulation plays a major role in protection against hyperammonemia.

Increases in walking distance in patients with peripheral vascular disease treated with L-carnitine: a double-blind, cross-over study

A double-blind, cross-over study was designed to evaluate the effects of L-carnitine in patients with peripheral vascular disease. After drug washout, 20 patients were randomly assigned to receive placebo or L-carnitine (2 g bid, orally) for a period of 3 weeks and were then crossed over to the other treatment for an additional 3 weeks. The effect on walking distance at the end of each treatment period was measured by treadmill test. Absolute walking distance rose from 174 +/- 63 m with placebo to 306 +/- 122 m (p less than .01) with carnitine. Biopsy of the ischemic muscle, carried out before and after 15 days of L-carnitine administration in four additional patients, showed that treatment significantly increased total carnitine levels. An additional goal of this study was to ascertain the effects of L-carnitine on the metabolic changes induced by exercise in the affected limb. In six patients under control conditions, arterial and popliteal venous lactate and pyruvate concentrations were determined at rest, when the maximal walking distance was reached, and 5 min after the walking test. Twenty-four hours later, L-carnitine was administered intravenously (3 g as a bolus followed by an infusion of 2 mg/kg/min for 30 min) and metabolic assessments were repeated. Five minutes after the walking test, popliteal venous lactate concentration increased by 107 +/- 16% before treatment and by only 54 +/- 32% (p less than .01) after carnitine. Furthermore, carnitine induced a more rapid recovery to the resting value of the lactate/pyruvate ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of L-carnitine on motility and acrosome reaction of human spermatozoa

L-carnitine added to the suspension medium decreases the glucose-sustained progressive motility of human spermatozoa. Addition of 20 mM L-carnitine to the capacitation medium causes an inhibition of the occurrence of the acrosome reaction parallel to a viability enhancement and negligible changes of the cellular content of ATP. The cellular efflux of glutamate-oxaloacetate transaminase was also inhibited by L-carnitine. A possible role of L-carnitine on membrane stability and metabolism of spermatozoa is briefly discussed.

Effect of methylglyoxal bis(guanylhydrazone) on hepatic, heart and skeletal muscle mitochondrial carnitine palmitoyltransferase and beta-oxidation of fatty acids

Methylglyoxal bis(guanylhydrazone) (MGBG) is an antileukemic agent and a structural polyamine analogue which inhibits S-adenosyl methionine decarboxylase. However, MGBG also produces profound mitochondrial structural damage and inhibition of fatty acid oxidation. Carnitine palmitoyltransferase-A (CPT-A) is located on the outer surface of the inner mitochondrial membrane and is the putative rate-controlling enzyme for mitochondrial long-chain fatty acid oxidation. The present experiments were designed to determine if MGBG inhibits CPT-A. Liver, heart and skeletal muscle mitochondria were isolated from rats following 24 hr of starvation. Measuring the reaction in the direction of palmitoylcarnitine plus CoA formation from palmitoyl-CoA plus carnitine ("forward reaction"), MGBG was competitive with l-carnitine. The MGBG CPT-A Ki values were (mM): liver, 5.0 +/- 0.6 (N = 15); heart 3.2 +/- 1.2 (N = 3); and skeletal muscle, 2.8 +/- 1.0 (N = 3). Lysis of hepatic mitochondria with Triton X-100 yielded a Ki of 4.0 +/- 2.0, which was not significantly different from intact mitochondria or inverted vesicles (4.9 mM). Purified hepatic CPT had a Ki of 4.2 mM. MGBG did not inhibit purified CPT in the "reverse reaction" (palmitoyl-CoA plus carnitine formation from palmitoylcarnitine plus CoA). Spermine and spermidine, which are structurally similar to MGBG, did not inhibit either CPT activity or acid-soluble product formation from 1-[14C]palmitoyl-CoA. MGBG inhibited mitochondrial state 3 oxidation rates of palmitoyl-CoA and palmitoylcarnitine, as well as of glutamate. However, the fatty acid substrates were considerably more sensitive than glutamate to MGBG inhibition. MGBG also increased hepatic mitochondrial aggregation which was reversed by l-carnitine. Fluorescence polarization, using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a probe, indicated that MGBG increased membrane rigidity in a dose-dependent manner. This effect was not altered by l-carnitine. MGBG also inhibited purified pigeon breast carnitine acetyltransferase (CAT; Ki = 1.6 mM). While MGBG appeared to be competitive with l-carnitine for both CPT and CAT, MGBG also exhibits a number of effects which may be mediated through membrane interaction and which are not reversed by carnitine.

L-carnitine effect on halothane-treated mitochondria

Addition of halothane to the incubation medium is shown to lower respiratory control and transmembrane potential and to increase ATPase activity in isolated rat liver mitochondria. Evidence is presented that L-carnitine is able to substantially decrease the negative effects of halothane on the energy-linked processes of mitochondria. The effects of halothane and the protective action of L-carnitine are discussed in the light of a possible involvement of long-chain acyl CoA in the unpairing of mitochondrial energy-linked functions.