Long-term effects of fatty acids on cell viability and gene expression of neonatal cardiac myocytes

A Pathophysiological Approach To Current Biomarkers

Biomarkers are necessary for screening and diagnosing numerous diseases, predicting the prognosis of patients, and following-up treatment and the course of the patient. Everyday new biomarkers are being used in clinics for these purposes. This section will discuss the physiological roles of the various current biomarkers in a healthy person and the pathophysiological mechanisms underlying the release of these biomarkers. This chapter aims to gain a new perspective for evaluating and interpreting the most current biomarkers.

Effects of fatty acids on inducing endoplasmic reticulum stress in bovine mammary epithelial cells

Fatty acids play important roles in the regulation of endoplasmic reticulum (ER) stress-induced apoptosis in different cells. Currently, the effects of fatty acids on bovine mammary epithelial cells (MEC) remain unknown. Our study examined bovine MEC viability and measured unfolded protein response (UPR)-related gene and protein expressions following fatty acid treatments. To evaluate the role of fatty acids, we treated MAC-T cells (a line of MEC) with 100 to 400 μM of saturated (palmitic and stearic acid) and unsaturated (palmitoleic, oleic, linoleic, and linolenic acid) fatty acids and 1 to 5 mM of short- and medium-chain fatty acids (acetic, propionic, butyric, and octanoic acid). Thereafter, we determined UPR-related gene expression using quantitative real-time PCR. Palmitic acid stimulated expression of XBP1s, ATF4, ATF6A, and C/EBP homologous protein (CHOP). Stearic acid increased expression of XBP1s and CHOP and decreased expression of ATF4 and ATF6A. Results of Western blot analysis and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay revealed that palmitic and stearic acid reduced MAC-T cell viability and induced extreme ER stress by increasing the protein expression of ER stress markers, such as phospho-PKR-like endoplasmic reticulum kinase, phospho-eIF2α, cleaved CASP-3, and CHOP. Among unsaturated long-chain fatty acids, palmitoleic acid increased expression of ATF4 and ATF6A. Oleic acid increased expression of XBP1s, ATF4, and ATF6A. Linoleic and linolenic acids increased expression of XBP1s, ATF4, and ATF6A but decreased expression of XBP1s and ATF6A at the highest dose. Although palmitoleic, oleic, and linoleic acid decreased CHOP expression, only palmitoleic acid increased MAC-T cell viability. Therefore, unsaturated long-chain fatty acids did not induce severe ER stress. Acetic, propionic, and butyric acids decreased expression of ATF4, ATF6A, and CHOP and increased XBP1s expression. Although only octanoic acid increased ATF4 and ATF6A expressions, it lowered expression of XBP1s and CHOP. Although fatty acid treatment did not increase the levels of ER stress proteins, butyric and octanoic acids reduced cell viability, possibly because of early differentiation. These results suggest that saturated fatty acids play important roles in MEC viability by inducing severe ER stress compared with unsaturated fatty acids. In addition, acetic and propionic acids (short- and medium-chain fatty acids) reduced ER stress. Therefore, the present study reflects the new insight that serum fatty acid concentration plays an important role in maintaining the lactation physiology of dairy cows.

Resveratrol prevents palmitic-acid-induced cardiomyocyte contractile impairment

Long-chain saturated fatty acids, especially palmitic acid (PA), contribute to cardiomyocyte lipotoxicity. This study tests the effects of PA on adult rat cardiomyocyte contractile function and proteins associated with calcium regulating cardiomyocyte contraction and relaxation. Adult rat cardiomyocytes were pretreated with resveratrol (Resv) and then treated with PA. For the reversal study, cardiomyocytes were incubated with PA prior to treatment with Resv. Cardiomyocyte contractility, ratio of rod- to round-shaped cardiomyocytes, and Hoechst staining were used to measure functional and morphological changes in cardiomyocytes. Protein expression of sarco-endoplasmic reticulum ATPase 2a (SERCA2a), native phospholamban (PLB) and phosphorylated PLB (pPLB ser16 and pPLB thr17), and troponin I (TnI) and phosphorylated TnI (pTnI) were measured. SERCA2a activity was also measured. Our results show that PA (200 μM) decreased the rate of cardiomyocyte relaxation, reduced the number of rod-shaped cardiomyocytes, and increased the number of cells with condensed nuclei; pre-treating cardiomyocytes with Resv significantly prevented these changes. Post-treatment with Resv did not reverse morphological changes induced by PA. Protein expression levels of SERCA2a, PLB, pPLBs, TnI, and pTnI were unchanged by PA or Resv. SERCA2a activity assay showed that V_max and Iono ratio were increased with PA and pre-treatment with Resv prevented this increase. In conclusion, our results show that Resv protect cardiomyocytes from contractile dysfunction induced by PA.

The paradox of obesity cardiomyopathy and the potential for weight loss as a therapy

Obesity is an independent risk factor for developing heart failure and the combination of the two disease states will prove to be a significant health burden over the coming years. Obesity is likely to contribute to the development of heart failure through a variety of mechanisms, including structural and functional changes, lipotoxicity and steatosis and altered substrate selection. However, once heart failure has developed, it seems that obesity confers a beneficial influence on prognosis in what has been termed the 'obesity paradox'. This may be a statistical phenomenon, but it should be considered that there is truly a protective state in the physiology of obesity. There is little evidence regarding the impact of weight loss in obese heart failure and whether or not this is beneficial. There have been small studies regarding the cardiovascular effects of both dietary weight loss and bariatric surgery, but few in heart failure. This is an important and increasingly relevant clinical question which must be addressed.

Structural and Metabolic Effects of Obesity on the Myocardium and the Aorta

Obesity per se is a recognized risk factor for cardiovascular disease exerting independent adverse effects on the cardiovascular system. Despite this well documented link, the mechanisms by which obesity modulates cardiovascular risk are not well understood. Obesity is linked to a wide variety of cardiac changes, from subclinical diastolic dysfunction to end stage systolic heart failure. In addition, obesity causes changes in cardiac metabolism that make ATP production and utilization less efficient producing functional consequences that are linked to the increased rate of heart failure in this population. This review focuses on the cardiovascular structural and metabolic remodelling that occurs in obesity with and without co-morbidities and the potential links to increased mortality in this population. © 2014 S. Karger GmbH, Freiburg.

Myocardial substrate metabolism in obesity

Obesity is linked to a wide variety of cardiac changes, from subclinical diastolic dysfunction to end-stage systolic heart failure. Obesity causes changes in cardiac metabolism, which make ATP production and utilization less efficient, producing functional consequences that are linked to the increased rate of heart failure in this population. As a result of the increases in circulating fatty acids and insulin resistance that accompanies excess fat storage, several of the proteins and genes that are responsible for fatty acid uptake and metabolism are upregulated, and the metabolic machinery responsible for glucose utilization and oxidation are inhibited. The resultant increase in fatty acid metabolism, and the inherent alterations in the proteins of the electron transport chain used to create the gradient needed to drive mitochondrial ATP production, results in a decrease in efficiency of cardiac work and a relative increase in oxygen usage. These changes in cardiac mitochondrial metabolism are potential therapeutic targets for the treatment and prevention of obesity-related heart failure.

Attenuation of the hypoxia-induced protein kinase Cdelta interaction with the 'd' subunit of F1Fo-ATP synthase in neonatal cardiac myocytes: implications for energy preservation and survival

The F1Fo-ATP synthase provides most of the heart's energy, yet events that alter its function during injury are poorly understood. Recently, we described a potent inhibitory effect on F1Fo-ATP synthase function mediated by the interaction of PKCdelta (protein kinase Cdelta) with dF1Fo ('d' subunit of the F1Fo-ATPase/ATP synthase). We have now developed novel peptide modulators which facilitate or inhibit the PKCdelta-dF1Fo interaction. These peptides include HIV-Tat (transactivator of transcription) protein transduction and mammalian mitochondrial-targeting sequences. Pre-incubation of NCMs (neonatal cardiac myocyte) with 10 nM extracellular concentrations of the mitochondrial-targeted PKCdelta-dF1Fo interaction inhibitor decreased Hx (hypoxia)-induced co-IP (co-immunoprecipitation) of PKCdelta with dF1Fo by 40+/-9%, abolished Hx-induced inhibition of F1Fo-ATPase activity, attenuated Hx-induced losses in F1Fo-derived ATP and protected against Hx- and reperfusion-induced cell death. A scrambled-sequence (inactive) peptide, which contained HIV-Tat and mitochondrial-targeting sequences, was without effect. In contrast, the cell-permeant mitochondrial-targeted PKCdelta-dF1Fo facilitator peptide, which we have shown previously to induce the PKCdelta-dF1Fo co-IP, was found to inhibit F1Fo-ATPase activity to an extent similar to that caused by Hx alone. The PKCdelta-dF1Fo facilitator peptide also decreased ATP levels by 72+/-18% under hypoxic conditions in the presence of glycolytic inhibition. None of the PKCdelta-dF1Fo modulatory peptides altered the inner mitochondrial membrane potential. Our studies provide the first evidence that disruption of the PKCdelta-dF1Fo interaction using cell-permeant mitochondrial-targeted peptides attenuates cardiac injury resulting from prolonged oxygen deprivation.

Signalling components involved in contraction-inducible substrate uptake into cardiac myocytes

Glucose and long-chain fatty acids (LCFA) are two major substrates used by heart and skeletal muscle to support contractile activity. In quiescent cardiac myocytes a substantial portion of the glucose transporter GLUT4 and the putative LCFA transporter fatty acid translocase (FAT)/CD36 are stored in intracellular compartments. Induction of cellular contraction by electrical stimulation results in enhanced uptake of both glucose and LCFA through translocation of GLUT4 and FAT/CD36 respectively to the sarcolemma. The involvement of protein kinase A, AMP-activated protein kinase (AMPK), protein kinase C (PKC) isoforms and the extracellular signal-regulated kinases was evaluated in cardiac myocytes as candidate signalling enzymes involved in recruiting these transporters in response to contraction. The collected evidence excluded the involvement of PKA and implicated an important role for AMPK and for one (or more) PKC isoform(s) in contraction-induced translocation of both GLUT4 and FAT/CD36. The unravelling of further components along this contraction pathway can provide valuable information on the coordinated regulation of the uptake of glucose and of LCFA by an increase in mechanical activity of heart and skeletal muscle.

NMR and cDNA array analysis prior to heart failure reveals an increase of unsaturated lipids, a glutamine/glutamate ratio decrease and a specific transcriptome adaptation in obese rat heart

Obesity is a risk factor for heart failure through a set of hemodynamic and hormonal adaptations, but its contribution at the molecular level is not clearly known. Therefore, we investigated the kinetic cardiac transcriptome and metabolome in the Spontaneous Hypertensive Heart Failure (SHHF) rat. The SHHF rat is devoid of leptin signaling when homozygous for a mutation of the leptin receptor (ObR) gene. The ObR-/- SHHF rat is obese at 4 months of age and prone to heart failure after 14 months whereas its lean counterpart ObR-/+ is prone to heart failure after 16 months. We used a set of rat pangenomic high-density macroarrays to monitor left ventricle cardiac transcriptome regulation in 4- and 10-month-old, lean and obese animals. Comparative analysis of left ventricle of 4- and 10-month-old lean rat revealed 222 differentially expressed genes while 4- and 10-month-old obese rats showed 293 differentially expressed genes. (1)H NMR analysis of the metabolome of left ventricular extracts displayed a global decrease of metabolites, except for taurine, and lipid concentration. This may be attributed to gene expression regulation and likely increased extracellular mass. The glutamine to glutamate ratio was significantly lower in the obese group. The relative unsaturation of lipids increased in the obese heart; in particular, omega-3 lipid concentration was higher in the 10-month-old obese heart. Overall, several specific kinetic molecular patterns act as a prelude to heart failure in the leptin signaling deficient SHHF obese rat.

Effect of Omacor on HRV parameters in patients with recent uncomplicated myocardial infarction - A randomized, parallel group, double-blind, placebo-controlled trial: study design [ISRCTN75358739]

BACKGROUND: A large body of data derived from animal, epidemiological and clinical studies indicate that n-3 polyunsaturated fatty acids have a favourable effect on the prognosis of patients with cardiovascular disease in general, and on reducing sudden death in particular.Depressed heart rate variability (HRV), an indicator of impairment of the autonomic nervous system, has been shown to be a powerful predictor of subsequent mortality in patients surviving an acute myocardial infarction. A multitude of studies have demonstrated this strong association, suggesting that the imbalance in the sympathic/parasympathetic system may facilitate emergence of ventricular arrhythmias.Heart rate variability parameters will be assessed in the present study, with the primary objective of evaluating the possible superiority of Omacor (a highly refined, concentrated omega-3 fatty acid) versus placebo in improving HRV from baseline to endpoint in patients with recent uncomplicated myocardial infarction. Both groups will receive optimal conventional treatment.The study will also explore and quantify improvement in time domain HRV indices and will assess the safety of administering Omacor to optimally treated post-infarction patients (conventional treatment). METHODS: This multi-centre study will evaluate the effect of Omacor 1 g, o.d. on time-domain HRV parameters in comparison to placebo o.d. in patients with recent uncomplicated transmural myocardial infarction.Patients will be screened during the first few days after the acute event as appropriate for the patient's condition, and after obtaining informed consent. Based on inclusion/exclusion criteria, a first 24-hour Holter recording will be performed. Two to five days later, screened patients still eligible for the study will undergo a second 24-hour Holter recording. After the second Holter recording, all patients will be randomly allocated to treatment with Omacor 1 g, o.d. or placebo o.d.One hundred patients will be followed in double-blind fashion for a six-month period after randomization. Visits, including 24-hour Holter recording and assessment of adverse events, will take place at one-month intervals +/- five days after randomization, i.e., six times in all.

Recent advances in mechanisms regulating glucose oxidation at the level of the pyruvate dehydrogenase complex by PDKs

The mitochondrial pyruvate dehydrogenase complex (PDC) catalyzes the oxidative decarboxylation of pyruvate, linking glycolysis to the tricarboxylic acid cycle and fatty acid (FA) synthesis. Knowledge of the mechanisms that regulate PDC activity is important, because PDC inactivation is crucial for glucose conservation when glucose is scarce, whereas adequate PDC activity is required to allow both ATP and FA production from glucose. The mechanisms that control mammalian PDC activity include its phosphorylation (inactivation) by a family of pyruvate dehydrogenase kinases (PDKs 1-4) and its dephosphorylation (activation, reactivation) by the pyruvate dehydrogenase phosphate phosphatases (PDPs 1 and 2). Isoform-specific differences in kinetic parameters, regulation, and phosphorylation site specificity of the PDKs introduce variations in the regulation of PDC activity in differing endocrine and metabolic states. In this review, we summarize recent significant advances in our knowledge of the mechanisms regulating PDC with emphasis on the PDKs, in particular PDK4, whose expression is linked with sustained changes in tissue lipid handling and which may represent an attractive target for pharmacological interventions aimed at modulating whole body glucose, lipid, and lactate homeostasis in disease states.

Critical steps in cellular fatty acid uptake and utilization

Despite decades of extensive research, the transport routes, mechanisms of uptake and points of flux control of long-chain fatty acids (FA) in mammalian organs are still incompletely understood. In non-fenestratred organs such as heart and skeletal muscle, membrane barriers for blood-borne FA are the luminal and abluminal membranes of endothelial cells, the sarcolemma and the mitochondrial membranes. Transport of FA through the phospholipid bilayer of the cellular membrane is most likely accomplished by diffusion of protonated FA. Evidence is accumulating that membrane-associated proteins, such as plasmalemmal fatty acid-binding protein (FABPpm) and fatty acid translocase (FAT/CD36), either alone or in conjunction with albumin binding protein (ABP), are instrumental in enhancing the delivery of FA to the cellular membrane. Inside the cell, cytoplasmic fatty acid-binding proteins (FABPc) are involved in diffusion of FA from the plasmalemma to the intracellular sites of conversion, such as the mitochondrial outer membrane. After conversion of FA to FACoA, the fatty acyl chain is transported across the mitochondrial inner membrane in a carnitine-mediated fashion. Uptake and utilization of FA by muscle cells are finely tuned, most likely to avoid the intracellular accumulation of FA, as these are cytotoxic at high concentrations. On a short-term basis, net uptake is, among others, regulated by intracellular translocation of FAT from intracellular stores to the sarcolemma and by the concentration gradient of FA across the sarcolemma. The latter implies that, among others, the rate of FA utilization determines the rate of uptake. The rate of utilization is governed by a variety of factors, including malonylCoA, the ratio acetylCoA/CoA and the availability of competing substrates such as glucose, lactate, and ketone bodies. Long-term regulation of uptake and utilization is accomplished by alterations in the rate of expression of genes, encoding for FA-handling proteins. Circumstantial evidence indicates that FA themselves are able to modulate the expression of FA-handling genes via nuclear transcription factors such as peroxisome proliferator-activated receptors (PPARs).

Transcriptional activation of energy metabolic switches in the developing and hypertrophied heart

1. The present review focuses on the gene regulatory mechanisms involved in the control of cardiac mitochondrial energy production in the developing heart and following the onset of pathological cardiac hypertrophy. Particular emphasis has been given to the mitochondrial fatty acid oxidation (FAO) pathway and its control by members of the nuclear receptor transcription factor superfamily. 2. During perinatal cardiac development, the heart undergoes a switch in energy substrate preference from glucose in the fetal period to fatty acids following birth. This energy metabolic switch is paralleled by changes in the expression of the enzymes and protein involved in the respective pathways. 3. The postnatal activation of the mitochondrial energy production pathway involves the induced expression of nuclear genes encoding FAO enzymes, as well as other proteins important in mitochondrial energy transduction/production pathways. Recent evidence indicates that this postnatal gene regulatory effect involves the actions of the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha) and its coactivator the PPARgamma coactivator 1 (PGC-1). 4. The PGC-1 not only activates PPARalpha to induce FAO pathway enzymes in the postnatal heart, but it also plays a pivotal role in the control of cardiac mitochondrial number and function. Thus, PGC-1 plays a master regulatory role in the high-capacity mitochondrial energy production system in the adult mammalian heart. 5. During the development of pathological forms of cardiac hypertrophy, such as that due to pressure overload, the myocardial energy substrate preference shifts back towards the fetal pattern, with a corresponding reduction in the expression of FAO enzyme genes. This metabolic shift is due to the deactivation of the PPARalpha/PGC-1 complex. 6. The deactivation of PPARalpha and PGC-1 during the development of cardiac hypertrophy involves regulation at several levels, including a reduction in the expression of these genes, as well as post-translational effects due to the mitogen-activated protein kinase pathway. Future studies aim at defining whether this transcriptional 'switch' and its effects on myocardial metabolism are adaptive or maladaptive in the hypertrophied heart.

A fatty acid desaturase modulates the activation of defense signaling pathways in plants

Salicylic acid (SA) plays an important role in activating various plant defense responses, including expression of the pathogenesis-related (PR) genes and systemic acquired resistance. A critical positive regulator of the SA signaling pathway in Arabidopsis is encoded by the NPR1 gene. However, there is growing evidence that NPR1-independent pathways can also activate PR expression and disease resistance. To elucidate the components associated with NPR1-independent defense signaling, we isolated a suppressor of the npr1-5 allele, designated ssi2. The recessive ssi2 mutation confers constitutive PR gene expression, spontaneous lesion formation, and enhanced resistance to Peronospora parasitica. In contrast, a subset of defense responses regulated by the jasmonic acid (JA) signaling pathway, including expression of the defensin gene PDF1.2 and resistance to Botrytis cinerea, is impaired in ssi2 plants. With the use of a map-based approach, the SSI2 gene was cloned and shown to encode a stearoyl-ACP desaturase (S-ACP DES). S-ACP DES is an archetypical member of a family of soluble fatty acid (FA) desaturases; these enzymes play an important role in regulating the overall level of desaturated FAs in the cell. The activity of mutant S-ACP DES enzyme was reduced 10-fold, resulting in elevation of the 18:0 FA content in ssi2 plants. Because reduced S-ACP DES activity leads to the induction of certain defense responses and the inhibition of others, we propose that a FA-derived signal modulates crosstalk between different defense signaling pathways.

Induction of cardiac FABP gene expression by long chain fatty acids in cultured rat muscle cells

The induction of cardiac FABP expression by long-chain fatty acids was measured in cultured rat myoblasts, myotubes and adult cardiomyocytes. With quantitative RT-PCR techniques, the primary transcription product of the FABP gene and the mature mRNA were measured. Incubations of 30 min resulted in a larger than 2-fold increase of the primary transcript in all cells, and FABP mRNA more than doubled in myoblasts and cardiomyocytes after 10 h of fatty acid exposure. The results demonstrate that long chain fatty acids induce the expression of the cardiac FABP gene in muscle cells and their undifferentiated precursors at the level of transcription initiation, suggesting that all factors involved in fatty acid dependent gene induction are already present in myoblasts. Thus, myoblast cell lines should be useful for the characterization of fatty acid response elements that control the expression of the FABP gene.

PPAR signaling in the control of cardiac energy metabolism

Cardiac energy metabolic shifts occur as a normal response to diverse physiologic and dietary conditions and as a component of the pathophysiologic processes which accompany cardiac hypertrophy, heart failure, and myocardial ischemia. The capacity to produce energy via the utilization of fats by the mammalian postnatal heart is controlled in part at the level of expression of nuclear genes encoding enzymes involved in mitochondrial fatty acid beta-oxidation (FAO). The principal transcriptional regulator of FAO enzyme genes is the peroxisome proliferator-activated receptor alpha (PPARalpha), a member of the ligand-activated nuclear receptor superfamily. Among the ligand activators of PPARalpha are long-chain fatty acids; therefore, increased uptake of fatty acid substrate into the cardiac myocyte induces a transcriptional response leading to increased expression of FAO enzymes. PPARalpha-mediated control of cardiac metabolic gene expression is activated during postnatal development, short-term starvation, and in response to exercise training. In contrast, certain pathophysiologic states, such as pressure overload-induced hypertrophy, result in deactivation of PPARalpha and subsequent dysregulation of FAO enzyme gene expression, which sets the stage for abnormalities in cardiac lipid homeostasis and energy production, some of which are influenced by gender. Thus, PPARalpha not only serves a critical role in normal cardiac metabolic homeostasis, but alterations in PPARalpha signaling likely contribute to the pathogenesis of a variety of disease states. PPARalpha as a ligand-activated transcription factor is a potential target for the development of new therapeutic strategies aimed at the prevention of pathologic cardiac remodeling.

Effects of fatty acids on uncoupling protein-2 expression in the rat heart

Fatty acids are thought to play a role in the activity of uncoupling proteins (UCP) and have been shown to regulate the expression of genes encoding proteins involved in fatty acid handling. Therefore, we investigated whether fatty acids, which are the main substrates for the heart, affect rat cardiac UCP-2 expression in vivo and in vitro. After birth, when the contribution of fatty acid oxidation to cardiac energy conversion increases, UCP-2 expression enhanced rapidly. In the adult heart, however, UCP-2 mRNA levels did not alter during conditions associated with either enhanced (fasting, diabetes) or decreased (hypertrophy) fatty acid utilization. Exposure of neonatal cardiomyocytes and embryonic rat heart-derived H9c2 cells to fatty acids (palmitic and oleic acid) for 48 h strongly induced UCP-2 expression. Stimulation of neonatal cardiomyocytes with triiodothyronine also increased UCP-2 mRNA levels, though only in the presence of fatty acids. Ligands specific to the fatty acid-activated transcription factor PPARalpha, but not to PPARgamma, acted as inducers of cardiomyocyte UCP-2 expression. It is concluded that fatty acids promote UCP-2 expression in neonatal cardiomyocytes, which might explain the rapid increase in UCP-2 mRNA in the postnatal heart. However, UCP-2 mRNA levels in the adult heart appear to be insensitive to changes in cardiac fatty acid handling under various pathological conditions.

Structure and chromosomal location of the rat gene encoding the heart fatty acid-binding protein

The gene coding for rat heart fatty acid-binding protein (FABP), along with 1.2 kb of its 5'-untranscribed region, was amplified by PCR, cloned and sequenced. As in other FABP genes, the coding sequence is interrupted by three introns of 3.4, 1.4 and 1.1 kb, respectively. Fluorescence in situ hybridization mapping revealed that the gene is located on chromosome 5q36. Using intron-specific primers flanking exon 2, unspliced primary transcript RNA of the FABP gene was detected in a preparation of total RNA isolated from rat heart, proving that the cloned gene is expressed in adult cardiac tissue.

Intracellular transport of fatty acids in muscle. Role of cytoplasmic fatty acid-binding protein

Long-chain fatty acids represent a major substrate for energy production in striated muscles, especially in those muscles which have a high oxidative enzymatic capacity. Following their uptake from the extracellular compartment the fatty acids have to translocate through the aqueous cytoplasm of the myocytes to reach the mitochondria where they undergo oxidative degradation. This intracellular transport is assisted by cytoplasmic fatty acid-binding protein (FABPc), a small (15 kD) protein which shows a high affinity for the non-covalent binding of long-chain fatty acids, and of which several types occur. So-called heart-type or muscle-type FABPc is found in muscle cells, and is abundant especially in oxidative fibers. The muscular FABPc content appears to relate to the rate of fatty acid utilization, and also changes in concert to modulations in fatty acid utilization induced by (patho)physiological stimuli (e.g. endurance training, diabetes). The facilitation of intracellular fatty acid transport by FABPc is accomplished by increasing the concentration of the diffusing fatty acids in the aqueous cytoplasm and, most likely, also by interacting directly with membranes to promote transfer of fatty acids to and from the cytosolic binding protein.