A high fat diet increases mitochondrial fatty acid oxidation and uncoupling to decrease efficiency in rat heart

Elevated levels of cardiac mitochondrial uncoupling protein 3 (UCP3) and decreased cardiac efficiency (hydraulic power/oxygen consumption) with abnormal cardiac function occur in obese, diabetic mice. To determine whether cardiac mitochondrial uncoupling occurs in non-genetic obesity, we fed rats a high fat diet (55% kcal from fat) or standard laboratory chow (7% kcal from fat) for 3 weeks, after which we measured cardiac function in vivo using cine MRI, efficiency in isolated working hearts and respiration rates and ADP/O ratios in isolated interfibrillar mitochondria; also, measured were medium chain acyl-CoA dehydrogenase (MCAD) and citrate synthase activities plus uncoupling protein 3 (UCP3), mitochondrial thioesterase 1 (MTE-1), adenine nucleotide translocase (ANT) and ATP synthase protein levels. We found that in vivo cardiac function was the same for all rats, yet oxygen consumption was 19% higher in high fat-fed rat hearts, therefore, efficiency was 21% lower than in controls. We found that mitochondrial fatty acid oxidation rates were 25% higher, and MCAD activity was 23% higher, in hearts from rats fed the high fat diet when compared with controls. Mitochondria from high fat-fed rat hearts had lower ADP/O ratios than controls, indicating increased respiratory uncoupling, which was ameliorated by GDP, a UCP3 inhibitor. Mitochondrial UCP3 and MTE-1 levels were both increased by 20% in high fat-fed rat hearts when compared with controls, with no significant change in ATP synthase or ANT levels, or citrate synthase activity. We conclude that increased cardiac oxygen utilisation, and thereby decreased cardiac efficiency, occurs in non-genetic obesity, which is associated with increased mitochondrial uncoupling due to elevated UCP3 and MTE-1 levels.

Cardiac response to hypobaric hypoxia: persistent changes in cardiac mass, function, and energy metabolism after a trek to Mt. Everest Base Camp

We postulated that changes in cardiac high-energy phosphate metabolism may underlie the myocardial dysfunction caused by hypobaric hypoxia. Healthy volunteers (n=14) were studied immediately before, and within 4 d of return from, a 17-d trek to Mt. Everest Base Camp (5300 m). (31)P magnetic resonance (MR) spectroscopy was used to measure cardiac phosphocreatine (PCr)/ATP, and MR imaging and echocardiography were used to assess cardiac volumes, mass, and function. Immediately after returning from Mt. Everest, total body weight had fallen by 3% (P<0.05), but left ventricular mass, adjusted for changes in body surface area, had disproportionately decreased by 11% (P<0.05). Alterations in diastolic function were also observed, with a reduction in peak left ventricular filling rates and mitral inflow E/A, by 17% (P<0.05) and 24% (P<0.01), respectively, with no change in hydration status. Compared with pretrek, cardiac PCr/ATP ratio had decreased by 18% (P<0.01). Whether the abnormalities were even greater at altitude is unknown, but all had returned to pretrek levels after 6 mo. The alterations in cardiac morphology, function, and energetics are similar to findings in patients with chronic hypoxia. Thus, a decrease in cardiac PCr/ATP may be a universal response to periods of sustained low oxygen availability, underlying hypoxia-induced cardiac dysfunction in healthy human heart and in patients with cardiopulmonary diseases.

The effect of high-altitude on human skeletal muscle energetics: P-MRS results from the Caudwell Xtreme Everest expedition

Many disease states are associated with regional or systemic hypoxia. The study of healthy individuals exposed to high-altitude hypoxia offers a way to explore hypoxic adaptation without the confounding effects of disease and therapeutic interventions. Using ³¹P magnetic resonance spectroscopy and imaging, we investigated skeletal muscle energetics and morphology after exposure to hypobaric hypoxia in seven altitude-naïve subjects (trekkers) and seven experienced climbers. The trekkers ascended to 5300 m while the climbers ascended above 7950 m. Before the study, climbers had better mitochondrial function (evidenced by shorter phosphocreatine recovery halftime) than trekkers: 16±1 vs. 22±2 s (mean ± SE, p<0.01). Climbers had higher resting [Pi] than trekkers before the expedition and resting [Pi] was raised across both groups on their return (PRE: 2.6±0.2 vs. POST: 3.0±0.2 mM, p<0.05). There was significant muscle atrophy post-CXE (PRE: 4.7±0.2 vs. POST: 4.5±0.2 cm², p<0.05), yet exercising metabolites were unchanged. These results suggest that, in response to high altitude hypoxia, skeletal muscle function is maintained in humans, despite significant atrophy.

Metabolic adaptation of skeletal muscle to high altitude hypoxia: how new technologies could resolve the controversies

In most tissues of the body, cellular ATP production predominantly occurs via mitochondrial oxidative phosphorylation of reduced intermediates, which are in turn derived from substrates such as glucose and fatty acids. In order to maintain ATP homeostasis, and therefore cellular function, the mitochondria require a constant supply of fuels and oxygen. In many disease states, or in healthy individuals at altitude, tissue oxygen levels fall and the cell must meet this hypoxic challenge to maintain energetics and limit oxidative stress. In humans at altitude and patients with respiratory disease, loss of skeletal muscle mitochondrial density is a consistent finding. Recent studies that have used cultured cells and genetic mouse models have elucidated a number of elegant adaptations that allow cells with a diminished mitochondrial population to function effectively in hypoxia. This article reviews these findings alongside studies of hypoxic human skeletal muscle, putting them into the context of whole-body physiology and acclimatization to high-altitude hypoxia. A number of current controversies are highlighted, which may eventually be resolved by a systems physiology approach that considers the time-or tissue-dependent nature of some adaptive responses. Future studies using high-throughput metabolomic, transcriptomic, and proteomic technologies to investigate hypoxic skeletal muscle in humans and animal models could resolve many of these controversies, and a case is therefore made for the integration of resulting data into computational models that account for factors such as duration and extent of hypoxic exposure, subjects' backgrounds, and whether data have been acquired from active or sedentary individuals. An integrated and more quantitative understanding of the body's metabolic response to hypoxia and the conditions under which adaptive processes occur could reveal much about the ways that tissues function in the very many disease states where hypoxia is a critical factor.

Studying Cerebellar Circuits by Remote Control of Selected Neuronal Types with GABA(A) Receptors

Although GABA_A receptor-mediated inhibition of cerebellar Purkinje cells by molecular layer interneurons (MLIs) has been studied intensely at the cellular level, it has remained unclear how this inhibition regulates cerebellum-dependent behaviour. We have implemented two complementary approaches to investigate the function of the MLI-Purkinje cell synapse on the behavioural level. In the first approach we permanently disrupted inhibitory fast synaptic transmission at the synapse by genetically removing the postsynaptic GABA_A receptors from Purkinje cells (PC-Δγ2 mice). We found that chronic disruption of the MLI-Purkinje cell synapse strongly impaired cerebellar learning of the vestibular occular reflex (VOR), presumably by disrupting the temporal patterns of Purkinje cell activity. However, in PC-Δγ2 mice the baseline VOR reflex was only mildly affected; indeed PC-Δγ2 mice show no ataxia or gait abnormalities, suggesting that MLI control of Purkinje cell activity is either not involved in ongoing motor tasks or that the system compensates for its loss. To investigate the latter possibility we developed an alternative genetic technique; we made the MLI-Purkinje cell synapse selectively sensitive to rapid manipulation with the GABA_A receptor modulator zolpidem (PC-γ2-swap mice). Minutes after intraperitoneal zolpidem injection, these PC-γ2-swap mice developed severe motor abnormalities, revealing a substantial contribution of the MLI-Purkinje cell synapses to real time motor control. The cell-type selective permanent knockout of synaptic GABAergic input and the fast reversible modulation of GABAergic input at the same synapse illustrate how pursuing both strategies gives a fuller view.

Human placental metabolic adaptation to chronic hypoxia, high altitude: hypoxic preconditioning

We have previously demonstrated placentas from laboring deliveries at high altitude have lower binding of hypoxia-inducible transcription factor (HIF) to DNA than those from low altitude. It has recently been reported that labor causes oxidative stress in placentas, likely due to ischemic hypoxic insult. We hypothesized that placentas of high-altitude residents acquired resistance, in the course of their development, to oxidative stress during labor. Full-thickness placental tissue biopsies were collected from laboring vaginal and nonlaboring cesarean-section term (37–41 wk) deliveries from healthy pregnancies at sea level and at 3,100 m. After freezing in liquid nitrogen within 5 min of delivery, we quantified hydrophilic and lipid metabolites using ³¹P and ¹H NMR metabolomics. Metabolic markers of oxidative stress, increased glycolysis, and free amino acids were present in placentas following labor at sea level, but not at 3,100 m. In contrast, at 3,100 m, the placentas were characterized by the presence of concentrations of stored energy potential (phosphocreatine), antioxidants, and low free amino acid concentrations. Placentas from pregnancies at sea level subjected to labor display evidence of oxidative stress. However, laboring placentas at 3,100 m have little or no oxidative stress at the time of delivery, suggesting greater resistance to ischemia-reperfusion. We postulate that hypoxic preconditioning might occur in placentas that develop at high altitude.

cGMP promotes neurite outgrowth and growth cone turning and improves axon regeneration on spinal cord tissue in combination with cAMP

Cyclic adenosine monophosphate (cAMP) has been intensively studied in recent years in order to elucidate its contribution in intracellular signalling mechanisms that regulate axon growth and guidance, and also to test if its activation can promote axon regeneration after injury. Cyclic guanosine monophosphate (cGMP), however, has been given considerably less attention even though it too mediates intracellular signalling cascades activated by extracellular guidance cues. cGMP can promote neurite outgrowth in neuronal cell lines but its role in promoting growth and regeneration of primary neurons is not well established. Here, we have examined the effects of elevating cGMP activity on axon growth, guidance and regeneration in vitro. We have found that, like cAMP elevation, activation of cGMP increases rat dorsal root ganglion (DRG) neurite outgrowth on a polylysine substrate and that asymmetric cGMP elevation promotes attractive growth cone turning. When grown in an in vitro model of axon regeneration activation of cGMP alone was not sufficient to promote adult neurite outgrowth. However, when combined with cAMP elevation substantial regeneration of adult neurites is achieved, superior to that achieved with either cAMP or cGMP alone. Regeneration is enhanced still further with simultaneous application of a Nogo receptor blocking peptide, suggesting this combinatorial strategy could achieve far greater axon regeneration in vivo than targeting individual cell signalling mechanisms.

Differential cross sections for the ionization of oriented H2 molecules by electron impact

A nonperturbative close-coupling technique is used to calculate differential cross sections for the electron-impact ionization of H2 at an energy of 35.4 eV. Our approach allows cross sections for any orientation of the molecule with respect to the incident electron beam to be analyzed. New features in the resulting cross sections are found compared with the case where the molecular orientation is averaged, and also with cross sections for He at equivalent electron kinematics. When averaged over all possible molecular orientations, good agreement is found with recent experimental results.

Pharmacological PKA inhibition: all may not be what it seems

Signaling through the cyclic adenosine monophosphate-dependent protein kinase [protein kinase A (PKA)] is an important and widely studied area of signal transduction research. This signaling pathway is commonly investigated through the use of the pharmacological PKA inhibitors H89 and KT 5720. Both of these compounds are thought to block PKA actions through competitive inhibition of the adenosine triphosphate site on the PKA catalytic subunit. Recently, a number of studies have identified actions of H89 and KT 5720 that are independent of their effects on PKA. These nonspecific effects are widespread; they include actions on other protein kinases and signaling molecules and also on basic cellular functions, such as transcription. Here, I summarize the nonspecific effects of these two compounds and compare their actions with those of other PKA inhibitors.

Increased mitochondrial uncoupling proteins, respiratory uncoupling and decreased efficiency in the chronically infarcted rat heart

Heart failure patients have abnormal cardiac high energy phosphate metabolism, the explanation for which is unknown. Patients with heart failure also have elevated plasma free fatty acid (FFA) concentrations. Elevated FFA levels are associated with increased cardiac mitochondrial uncoupling proteins (UCPs), which, in turn, are associated with decreased mitochondrial respiratory coupling and low cardiac efficiency. Here, we determined whether increased mitochondrial UCP levels contribute to decreased energetics in the failing heart by measuring UCPs and respiration in mitochondria isolated from the viable myocardium of chronically infarcted rat hearts and measuring efficiency (hydraulic work/O(2) consumption) in the isolated, working rat heart. Ten weeks after infarction, cardiac levels of UCP3 were increased by 53% in infarcted, failing hearts that had ejection fractions less than 45%. Cardiac UCP3 levels correlated positively with non-fasting plasma FFAs (r=0.81; p<0.01). Mitochondria from failing hearts were less coupled than those from control hearts, as demonstrated by the lower ADP/O ratio of 1.9+/-0.1 compared with 2.5+/-0.2 in controls (p<0.05). The decreased ADP/O ratio was reflected in an efficiency of 14+/-2% in the failing hearts when perfused with 1 mM palmitate, compared with 20+/-1% in controls (p<0.05). We conclude that failing hearts have increased UCP3 levels that are associated with high circulating FFA concentrations, mitochondrial uncoupling, and decreased cardiac efficiency. Thus, respiratory uncoupling may underlie the abnormal energetics and low efficiency in the failing heart, although whether this is maladaptive or adaptive would require direct investigation.

Mitochondria and heart failure

PURPOSE OF REVIEW

Energetic abnormalities in cardiac and skeletal muscle occur in heart failure and correlate with clinical symptoms and mortality. It is likely that the cellular mechanism leading to energetic failure involves mitochondrial dysfunction. Therefore, it is crucial to elucidate the causes of mitochondrial myopathy, in order to improve cardiac and skeletal muscle function, and hence quality of life, in heart failure patients.

RECENT FINDINGS

Recent studies identified several potential stresses that lead to mitochondrial dysfunction in heart failure. Chronically elevated plasma free fatty acid levels in heart failure are associated with decreased metabolic efficiency and cellular insulin resistance. Tissue hypoxia, resulting from low cardiac output and endothelial impairment, can lead to oxidative stress and mitochondrial DNA damage, which in turn causes dysfunction and loss of mitochondrial mass. Therapies aimed at protecting mitochondrial function have shown promise in patients and animal models with heart failure.

SUMMARY

Despite current therapies, which provide substantial benefit to patients, heart failure remains a relentlessly progressive disease, and new approaches to treatment are necessary. Novel pharmacological agents are needed that optimize substrate metabolism and maintain mitochondrial integrity, improve oxidative capacity in heart and skeletal muscle, and alleviate many of the clinical symptoms associated with heart failure.

Rosiglitazone treatment improves cardiac efficiency in hearts from diabetic mice

Isolated perfused hearts from type 2 diabetic (db/db) mice show impaired ventricular function, as well as altered cardiac metabolism. Assessment of the relationship between myocardial oxygen consumption (MVO(2)) and ventricular pressure-volume area (PVA) has also demonstrated reduced cardiac efficiency in db/db hearts. We hypothesized that lowering the plasma fatty acid supply and subsequent normalization of altered cardiac metabolism by chronic treatment with a peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist will improve cardiac efficiency in db/db hearts. Rosiglitazone (23 mg/kg body weight/day) was administered as a food admixture to db/db mice for five weeks. Ventricular function and PVA were assessed using a miniaturized (1.4 Fr) pressure-volume catheter; MVO(2) was measured using a fibre-optic oxygen sensor. Chronic rosiglitazone treatment of db/db mice normalized plasma glucose and lipid concentrations, restored rates of cardiac glucose and fatty acid oxidation, and improved cardiac efficiency. The improved cardiac efficiency was due to a significant decrease in unloaded MVO(2), while contractile efficiency was unchanged. Rosiglitazone treatment also improved functional recovery after low-flow ischemia. In conclusion, the present study demonstrates that in vivo PPARgamma-treatment restores cardiac efficiency and improves ventricular function in perfused hearts from type 2 diabetic mice.

Fatty acid transporter levels and palmitate oxidation rate correlate with ejection fraction in the infarcted rat heart

OBJECTIVES

Cardiac fatty acid uptake occurs predominantly via sarcolemmal transporter proteins; fatty acid translocase (FAT/CD36), plasma membrane fatty acid binding protein (FABPpm) and fatty acid transporter proteins (FATP) 1 and 6. We hypothesised that levels of the fatty acid transporters would be reduced in the chronically infarcted rat heart, in parallel with reduced dependence on fatty acid utilisation.

METHODS AND RESULTS

In vivo left ventricular ejection fractions, measured using echocardiography, were 36% lower in rats six months after coronary artery ligation than in sham-operated control rats. In isolated, perfused, infarcted hearts, 3H-palmitate oxidation was 30% lower, and correlated with in vivo ejection fractions. As myocardial lipid incorporation was also reduced by 25%, total palmitate utilisation was 29% lower in the infarcted rat heart. The protein levels of the cardiac fatty acid transporters were reduced in the infarcted rat heart; FAT/CD36 by 36%, FABPpm by 12%, FATP6 by 21% and FATP1 by 26%, and the cytosolic fatty acid binding protein (cFABP) was 47% lower than in sham-operated rat hearts. Fatty acid transporter levels correlated with both palmitate oxidation rates and cardiac ejection fractions.

CONCLUSIONS

Reductions in fatty acid oxidation and lipid incorporation rates were accompanied by downregulation of the cardiac fatty acid transporters. The metabolic shift away from fatty acid utilisation was proportional to the degree of functional impairment in the chronically infarcted rat heart.

Insulin resistance, abnormal energy metabolism and increased ischemic damage in the chronically infarcted rat heart

OBJECTIVE

Many patients with heart failure have whole-body insulin resistance and reduced cardiac fluorodeoxyglucose uptake, but whether these metabolic changes have detrimental effects on the heart is unknown. Here, we tested whether there is a link between insulin resistance and ischemic damage in the chronically infarcted Wistar rat heart, postulating that the heart would have decreased insulin sensitivity, with lower GLUT4 glucose transporter protein levels due to high circulating free fatty acid (FFA) concentrations. A decreased capacity for glucose uptake would lower glycolytic adenosine triphosphate (ATP) production and thereby increase ischemic injury in the infarcted heart.

METHODS AND RESULTS

In vivo left ventricular ejection fractions, measured using echocardiography, were 40% lower in rats 10 weeks after coronary artery ligation than in sham-operated control rats. Insulin-stimulated D[2-3H]glucose uptake was 42% lower in isolated, perfused, infarcted hearts. Myocardial GLUT4 glucose transporter protein levels were 28% lower in the infarcted hearts and correlated negatively with ejection fractions and with fasting plasma FFA concentrations. Compared with controls, chronically infarcted hearts had 46% lower total glucose uptake and three-fold faster ATP hydrolysis rates, measured using phosphorus-31 nuclear magnetic resonance spectroscopy, during 32-min ischemia at 0.4 ml/min/gww. During reperfusion, recovery of left ventricular developed pressure in infarcted hearts was 42% lower than in control hearts.

CONCLUSIONS

Glucose uptake, in response to insulin or ischemia, was lower in the chronically infarcted rat heart and associated with increased circulating FFA concentrations and decreased GLUT4 levels. Thus, infarcted hearts had greater ATP depletion, and consequently incurred greater damage, during ischemia.

A case of multiple cutaneous schwannomas; schwannomatosis or neurofibromatosis type 2?

A 54 year old man presented with numerous cutaneous schwannomas, cranial nerve lesions, and spinal cord lesions, but no evidence of vestibular nerve involvement. There was no family history of neurocutaneous lesions. To help discriminate between the various possible diagnoses in this patient, molecular analysis of two cutaneous schwannomas was undertaken. An identical point mutation in the NF2 gene in the two anatomically distinct tumours was found, confirming this as a case of NF2 mosaicism.

Plasma free fatty acids and peroxisome proliferator-activated receptor alpha in the control of myocardial uncoupling protein levels

Diabetic patients have abnormal cardiac energy metabolism associated with high plasma free fatty acid (FFA) concentrations. We investigated whether high plasma FFAs increase mitochondrial uncoupling protein (UCP) levels in the mouse heart by activating the nuclear transcription factor peroxisome proliferator-activated receptor (PPAR)alpha. We used Western blotting to measure UCP protein levels in isolated cardiac mitochondria from PPARalpha-/- and diabetic mice. Cardiac UCP2 and UCP3 were significantly lower in the PPARalpha-/- mouse than in the wild type. Treatment with the PPARalpha-specific agonist, WY-14,643, increased cardiac UCP2 and UCP3 levels in wild-type mice but did not alter UCP levels in PPARalpha-/- mice. Inhibition of beta-oxidation with etomoxir increased cardiac UCP2 and UCP3 levels in wild-type mice and UCP2 levels in PPARalpha-/- mice but did not alter UCP3 levels in PPARalpha-/- mice. Streptozotocin treatment, which increased circulating FFAs by 91%, did not alter cardiac UCP2 levels in wild-type or PPARalpha-/- mice but increased UCP3 levels in wild-type, and not in PPARalpha-/-, mice. The diabetic db/db mouse had 50% higher plasma FFA concentrations and elevated cardiac UCP2 and UCP3 protein levels. We conclude that high plasma FFAs activated PPARalpha to increase cardiac UCP3 levels, but cardiac UCP2 levels changed via PPARalpha-dependent and -independent mechanisms.

A new low-cost hairtube design for the detection of the spotted-tailed quoll Dasyurus maculatus in south-eastern Australia

THE spotted-tailed quoll (Dasyurus maculatus) is the largest carnivorous marsupial extant on mainland Australia, where it has a fragmented distribution in forested habitats in the eastern part of the continent. This species is also found in Tasmania. D. maculatus have been found in a wide variety of forest types from sea level to over 1400 m above sea level, in areas generally receiving in excess of 600 mm of rainfall (Mansergh 1983). The distribution of D. maculatus is believed to have declined by over 50% following European settlement (Mansergh 1983).

The contribution of spotted-tailed quolls (Dasyurus maculatus) to the transmission of Echinococcus granulosus in the Byadbo Wilderness Area, Kosciuszko National Park, Australia

Scats were collected from 19 wild spotted-tailed quolls (Dasyurus maculatus) caught in a region of south-eastern mainland Australia where hydatidosis (Echinococcus granulosus) occurs commonly in swamp wallabies (Wallabia bicolour) and other wildlife. All scats were tested for coproantigens of E. granulosus tapeworms. None of the scats tested had detectable coproantigens of E. granulosus. These data and previous unsuccessful attempts to experimentally infect other species of dasyruid with E. granulosus suggest that spotted-tailed quolls may be refractory to infection with E. granulosus.

Uncoupling proteins in human heart

Abnormal energetic activity in heart failure correlates inversely with plasma free-fatty-acid concentrations. However, the link between energetic and metabolic abnormalities is unknown. To investigate this association, we obtained blood samples from 39 patients undergoing coronary artery bypass graft surgery. Patients fasted overnight before samples were taken. When plasma free-fatty-acid concentrations were raised, cardiac mitochondrial uncoupling proteins (UCP) increased (isoform UCP2, p<0.0001; isoform UCP3, p=0.0036) and those of glucose transporter (GLUT4) protein decreased (cardiac, p=0.0001; skeletal muscle, p=0.0006). Consequently, energy deficiency in heart failure might result from increased mitochondrial UCPs (ie, less efficient ATP synthesis) and depleted GLUT4 (ie, reduced glucose uptake). New treatment to correct these energy defects would be to simultaneously lower plasma free fatty acids and provide an alternative energy source.

Potential impact of aerial baiting for wild dogs on a population of spotted-tailed quolls (Dasyurus maculatus)

The spotted-tailed quoll (Dasyurus maculatus) is a threatened marsupial that inhabits forests in eastern Australia. In many of these forests the species is sympatric with populations of wild dogs (Canis lupus dingo, Canis familiaris and hybrids of the two), which are subject to poison-baiting programs. Many of these programs involve dropping meat baits injected with 6 mg of 1080 from helicopters. To date, the effect of this method on populations of spotted-tailed quolls has not been quantified. We carried out a simulated aerial baiting program using meat baits injected with a non-toxic baitmarker, Rhodamine B, which is laid down in the vibrissae of mammals ingesting baits. Of the 16 spotted-tailed quolls subsequently captured, 10 had Rhodamine B in their vibrissae. The potential impact that this level of bait uptake might have on a population of quolls is discussed.

A study of metabolic compartmentation in the rat heart and cardiac mitochondria using high-resolution magic angle spinning 1H NMR spectroscopy

High-resolution magic angle spinning (MAS) (1)H nuclear magnetic resonance (NMR) spectroscopy is increasingly being used to monitor metabolic abnormalities within cells and intact tissues. Many toxicological insults and metabolic diseases affect subcellular organelles, particularly mitochondria. In this study high-resolution (1)H NMR spectroscopy was used to examine metabolic compartmentation between the cytosol and mitochondria in the rat heart to investigate whether biomarkers of mitochondrial dysfunction could be identified and further define the mitochondrial environment. High-resolution MAS spectra of mitochondria revealed NMR signals from lactate, alanine, taurine, choline, phosphocholine, creatine, glycine and lipids. However, spectra from mitochondrial extracts contained additional well-resolved resonances from valine, methionine, glutamine, acetoacetate, succinate, and aspartate, suggesting that a number of metabolites bound within the mitochondrial membranes occur in 'NMR invisible' environments. This effect was further investigated using diffusion-weighted measurements of water and NMR spectroscopy during state 2 and state 3 respiration. State 3 respiration caused a decrease in the resonance intensity of endogenous succinate compared with state 2 respiration, suggesting that coupled respiration may also modulate the NMR detection of metabolites within mitochondria.