Functional compartmentation of glycolytic versus oxidative metabolism in isolated rabbit heart

Network models of protein phosphorylation, acetylation, and ubiquitination connect metabolic and cell signaling pathways in lung cancer

We analyzed large-scale post-translational modification (PTM) data to outline cell signaling pathways affected by tyrosine kinase inhibitors (TKIs) in ten lung cancer cell lines. Tyrosine phosphorylated, lysine ubiquitinated, and lysine acetylated proteins were concomitantly identified using sequential enrichment of post translational modification (SEPTM) proteomics. Machine learning was used to identify PTM clusters that represent functional modules that respond to TKIs. To model lung cancer signaling at the protein level, PTM clusters were used to create a co-cluster correlation network (CCCN) and select protein-protein interactions (PPIs) from a large network of curated PPIs to create a cluster-filtered network (CFN). Next, we constructed a Pathway Crosstalk Network (PCN) by connecting pathways from NCATS BioPlanet whose member proteins have PTMs that co-cluster. Interrogating the CCCN, CFN, and PCN individually and in combination yields insights into the response of lung cancer cells to TKIs. We highlight examples where cell signaling pathways involving EGFR and ALK exhibit crosstalk with BioPlanet pathways: Transmembrane transport of small molecules; and Glycolysis and gluconeogenesis. These data identify known and previously unappreciated connections between receptor tyrosine kinase (RTK) signal transduction and oncogenic metabolic reprogramming in lung cancer. Comparison to a CFN generated from a previous multi-PTM analysis of lung cancer cell lines reveals a common core of PPIs involving heat shock/chaperone proteins, metabolic enzymes, cytoskeletal components, and RNA-binding proteins. Elucidation of points of crosstalk among signaling pathways employing different PTMs reveals new potential drug targets and candidates for synergistic attack through combination drug therapy.

The Na+/K+ pump dominates control of glycolysis in hippocampal dentate granule cells

Cellular ATP that is consumed to perform energetically expensive tasks must be replenished by new ATP through the activation of metabolism. Neuronal stimulation, an energetically demanding process, transiently activates aerobic glycolysis, but the precise mechanism underlying this glycolysis activation has not been determined. We previously showed that neuronal glycolysis is correlated with Ca2+ influx, but is not activated by feedforward Ca2+ signaling (Díaz-García et al., 2021a). Since ATP-powered Na+ and Ca2+ pumping activities are increased following stimulation to restore ion gradients and are estimated to consume most neuronal ATP, we aimed to determine if they are coupled to neuronal glycolysis activation. By using two-photon imaging of fluorescent biosensors and dyes in dentate granule cell somas of acute mouse hippocampal slices, we observed that production of cytoplasmic NADH, a byproduct of glycolysis, is strongly coupled to changes in intracellular Na+, while intracellular Ca2+ could only increase NADH production if both forward Na+/Ca2+ exchange and Na+/K+ pump activity were intact. Additionally, antidromic stimulation-induced intracellular [Na+] increases were reduced >50% by blocking Ca2+ entry. These results indicate that neuronal glycolysis activation is predominantly a response to an increase in activity of the Na+/K+ pump, which is strongly potentiated by Na+ influx through the Na+/Ca2+ exchanger during extrusion of Ca2+ following stimulation.

Heart failure in diabetes

Heart failure and cardiovascular disorders represent the leading cause of death in diabetic patients. Here we present a systematic review of the main mechanisms underlying the development of diabetic cardiomyopathy. We also provide an excursus on the relative contribution of cardiomyocytes, fibroblasts, endothelial and smooth muscle cells to the pathophysiology of heart failure in diabetes. After having described the preclinical tools currently available to dissect the mechanisms of this complex disease, we conclude with a section on the most recent updates of the literature on clinical management.

With a grain of salt: Sodium elevation and metabolic remodelling in heart failure

Elevated intracellular Na (Na_i) and metabolic impairment are interrelated pathophysiological features of the failing heart (HF). There have been a number of studies showing that myocardial sodium elevation subtly affects mitochondrial function. During contraction, mitochondrial calcium (Ca_mito) stimulates a variety of TCA cycle enzymes, thereby providing reducing equivalents to maintain ATP supply. Na_i elevation has been shown to impact Ca_mito; however, whether metabolic remodelling in HF is caused by increased Na_i has only been recently demonstrated. This novel insight may help to elucidate the contribution of metabolic remodelling in the pathophysiology of HF, the lack of efficacy of current HF therapies and a rationale for the development of future metabolism-targeting treatments. Here we review the relationship between Na pump inhibition, elevated Na_i, and altered metabolic profile in the context of HF and their link to metabolic (in)flexibility and mitochondrial reprogramming.

Role of the Heart in Lactate Shuttling

After almost a century of misunderstanding, it is time to appreciate that lactate shuttling is an important feature of energy flux and metabolic regulation that involves a complex series of metabolic, neuroendocrine, cardiovascular, and cardiac events in vivo. Cell–cell and intracellular lactate shuttles in the heart and between the heart and other tissues fulfill essential purposes of energy substrate production and distribution as well as cell signaling under fully aerobic conditions. Recognition of lactate shuttling came first in studies of physical exercise where the roles of driver (producer) and recipient (consumer) cells and tissues were obvious. One powerful example of cell–cell lactate shuttling was the exchange of carbohydrate energy in the form of lactate between working limb skeletal muscle and the heart. The exchange of mass represented a conservation of mass that required the integration of neuroendocrine, autoregulatory, and cardiovascular systems. Now, with greater scrutiny and recognition of the effect of the cardiac cycle on myocardial blood flow, there brings an appreciation that metabolic fluxes must accommodate to pressure-flow realities within an organ in which they occur. Therefore, the presence of an intra-cardiac lactate shuttle is posited to explain how cardiac mechanics and metabolism are synchronized. Specifically, interruption of blood flow during the isotonic phase of systole is supported by glycolysis and subsequent return of blood flow during diastole allows for recovery sustained by oxidative metabolism.

Adiponectin protects HL-1 cardiomyocytes against rotenone-induced cytotoxicity through AMPK activation

The relationship between mitochondrial dysfunction or ER stress with pathogenesis of cardiovascular disease is well documented, but the crosstalk between them in cardiovascular diseases is not clear. Adiponectin (APN) is reported to become a potential cardioprotective molecule, but whether and how APN regulates mitochondrial dysfunction and ER stress is not clear. In this study, we used rotenone-treated HL-1 atrial cardiomyocytes as an in vitro model of mitochondrial dysfunction to investigate the possible interactions between mitochondrial dysfunction and ER stress and explore the effects of APN on rotenone-induced cytotoxicity and the underlying mechanisms. It found that rotenone treatment significantly activated the ER stress PRK-like endoplasmic reticulum kinase (PERK)-dependent pathway, decreased autophagic flux and APN expression in a dose-dependent manner. Pretreatment of GSK2606414, an inhibitor of PERK kinase activity, attenuated the rotenone-induced decrease of APN expression. In return exogenous APN pretreatment inhibited rotenone-induced ER stress and activated autophagy via AMP-activated protein kinase (AMPK) activation and protected HL-1 cells against apoptosis and enhanced the viability after rotenone treatment. In conclusion, rotenone treatment induced significant cardiomyocyte cytotoxicity and ER stress, suppressed autophagy, and decreased APN expression in HL-1 cells. APN in return inhibited ER stress and activated autophagy through AMPK activation, thus alleviating rotenone induced HL-1 apoptosis.

Akt is a critical node of acute myocardial insulin resistance and cardiac dysfunction after cardiopulmonary bypass

AIMS

Acute myocardial insulin resistance is an independent risk factor for patients who undergo cardiac surgery with cardiopulmonary bypass (CPB). However, the underlying mechanism of insulin resistance during CPB has not been fully investigated.

MATERIALS AND METHODS

To explore the role of myocardial insulin resistance on the cardiac function and its underlying mechanism, CPB operation and pharmacological intervention were applied in mini pigs, and myocardial insulin signaling, glucose uptake, ATP production and cardiac function were examined.

KEY FINDINGS

Our data showed that CPB elicited not only hyperglycemia and hyperinsulinemia, but also inactivated Akt, and impaired the transposition of membrane glucose transporter-4 (GLUT-4), reduced glucose uptake and ATP production in the myocardium as well, which in turn was accompanied with cardiac dysfunction. Meanwhile, linear correlations were established among reduced myocardial glucose uptake, ATP production, and depressed cardiac systolic or diastolic function. Reactivation of Akt by SC79, an Akt agonist, partially alleviated myocardial insulin resistance and restored post CPB cardiac function via augmenting myocardial glucose uptake and ATP production.

SIGNIFICANCE

These findings revealed that acute myocardial insulin resistance due to inactivation of Akt played a key role in cardiac dysfunction post CPB via suppressing glucose metabolism related energy supply.

Resistance of Fetal Guinea Pig Ventricular Myocardium to Hypoxia: Maintained Intracellular ATP Prevents the Opening of ATP-Sensitive Potassium Channels

The presence and function of the ATP-sensitive potassium channel current (I_KATP) were examined in the guinea pig myocardium to clarify the mechanisms for the resistance of the fetal myocardium to hypoxia. Experimental hypoxia markedly reduced the action potential duration and contractile force in isolated ventricular myocardium from the adult, but only moderately in those from the fetus. In isolated ventricular cardiomyocytes, the density of the I_KATP activated by cromakalim, as well as their sensitivity to intracellular ATP concentration, were not different between the fetus and adult. The tissue ATP content was similar between the fetal and adult myocardium under normal condition, but the hypoxia-induced decrease was smaller in the fetus. Confocal microscopic analysis revealed that the mitochondria in the fetal cardiomyocyte is less in quantity than that in the adult and is more localized to the cell center. These results indicate that I_KATP in the fetal guinea pig myocardium has a current density and ATP sensitivity similar to those of the adult, but is not activated under hypoxic conditions because the energy metabolism of the fetal myocardium is less dependent on oxidative phosphorylation.

AMPK-mediated degradation of Nav1.5 through autophagy

The voltage-gated cardiac sodium channel, Nav1.5, is the key component that controls cardiac excitative electrical impulse and propagation. However, the dynamic alterations of Nav1.5 during cardiac ischemia and reperfusion (I/R) are seldom reported. We found that the protein levels of rat cardiac Nav1.5 were significantly decreased in response to cardiac I/R injury. By simulating I/R injury in cells through activating AMPK by glucose deprivation, AMPK activator treatment, or hypoxia and reoxygenation (H/R), we found that Nav1.5 was down-regulated by AMPK-mediated autophagic degradation. Furthermore, AMPK was found to phosphorylate Nav1.5 at threonine (T) 101, which then regulates the interaction between Nav1.5 and the autophagic adaptor protein, microtubule-associated protein 1 light chain 3 (LC3), by exposing the LC3-interacting region adjacent to T101 in Nav1.5. This study highlights an instrumental role of AMPK in mediating the autophagic degradation of Nav1.5 during cardiac I/R injury.-Liu, X., Chen, Z., Han, Z., Liu, Y., Wu, X., Peng, Y., Di, W., Lan, R., Sun, B., Xu, B., Xu, W. AMPK-mediated degradation of Nav1.5 through autophagy.

The Plastidic Sugar Transporter pSuT Influences Flowering and Affects Cold Responses

Sucrose (Suc) is one of the most important types of sugars in plants, serving inter alia as a long-distance transport molecule, a carbon and energy storage compound, an osmotically active solute, and fuel for many anabolic reactions. Suc biosynthesis and degradation pathways are well known; however, the regulation of Suc intracellular distribution is poorly understood. In particular, the cellular function of chloroplast Suc reserves and the transporters involved in accumulating these substantial Suc levels remain uncharacterized. Here, we characterize the plastidic sugar transporter (pSuT) in Arabidopsis (Arabidopsis thaliana), which belongs to a subfamily of the monosaccharide transporter-like family. Transport analyses with yeast cells expressing a truncated, vacuole-targeted version of pSuT indicate that both glucose and Suc act as substrates, and nonaqueous fractionation supports a role for pSuT in Suc export from the chloroplast. The latter process is required for a correct transition from vegetative to reproductive growth and influences inflorescence architecture. Moreover, pSuT activity affects freezing-induced electrolyte release. These data further underline the central function of the chloroplast for plant development and the modulation of stress tolerance.

GPR35 promotes glycolysis, proliferation, and oncogenic signaling by engaging with the sodium potassium pump

The sodium potassium pump (Na/K-ATPase) ensures the electrochemical gradient of a cell through an energy-dependent process that consumes about one-third of regenerated ATP. We report that the G protein-coupled receptor GPR35 interacted with the α chain of Na/K-ATPase and promotes its ion transport and Src signaling activity in a ligand-independent manner. Deletion of Gpr35 increased baseline Ca²⁺ to maximal levels and reduced Src activation and overall metabolic activity in macrophages and intestinal epithelial cells (IECs). In contrast, a common T108M polymorphism in GPR35 was hypermorphic and had the opposite effects to Gpr35 deletion on Src activation and metabolic activity. The T108M polymorphism is associated with ulcerative colitis and primary sclerosing cholangitis, inflammatory diseases with a high cancer risk. GPR35 promoted homeostatic IEC turnover, whereas Gpr35 deletion or inhibition by a selective pepducin prevented inflammation-associated and spontaneous intestinal tumorigenesis in mice. Thus, GPR35 acts as a central signaling and metabolic pacesetter, which reveals an unexpected role of Na/K-ATPase in macrophage and IEC biology.

Antibacterial properties of nanofibers containing chrysanthemum essential oil and their application as beef packaging

This study was aimed to develop novel antibacterial packaging materials in order to reduce the microbial contamination of food surface. Chrysanthemum essential oil (CHEO) was successfully incorporated into chitosan nanofibers (CS/NF) through electrospinning which was demonstrated by SEM and AFM analysis. The antibacterial mechanism of CHEO against Listeria monocytogenes (L. monocytogenes) was explored as well. The cell membrane permeability of L. monocytogenes appeared to be increased by CHEO. In addition, respiratory metabolism of L. monocytogenes was inhibited by CHEO through the inhibition of the Embden-Meyerhof-Parnas (EMP) pathway. The presence of CHEO had a negative effect on the activity of hexokinase, phosphofructokinase and pyruvate kinase in L. monocytogenes cells. Release efficiency study indicated that the CHEO could be released slowly from CHEO/CS/NF to achieve long-lasting antibacterial effect. The antibacterial application of the CHEO nanofibers against L. monocytogenes was tested on beef, with an inhibition rate of 99.91%, 99.97%, and 99.95% at the temperature of 4 °C, 12 °C and 25 °C, respectively, after 7 days of storage. Beef parameters like thiobarbituric acid reactive substances (TBARS), pH values, and texture at different storage temperatures (4 °C, 12 °C and 25 °C) were evaluated as well. Due to the presence of antioxidant components in CHEO released from CHEO/CS/NF, the TBARS value in treated beef was 0.135 MDA/kg lower (P < 0.05) than the untreated sample at 4 °C after 12 days. PH value assay indicated that PH value of beef sample packed with CHEO/CS/NF (6.43) was lower than unpacked sample (7.05) at 4 °C after 10 days of storage. These obtained results all illustrated the fact that CHEO/CS/NF could prolong the shelf-life of beef, suggesting a potential application in food packaging.

Is there a causal link between intracellular Na elevation and metabolic remodelling in cardiac hypertrophy?

Alterations in excitation–contraction coupling and elevated intracellular sodium (Na_i) are hallmarks of pathological cardiac remodelling that underline contractile dysfunction. In addition, changes in cardiac metabolism are observed in cardiac hypertrophy and heart failure (HF) that lead to a mismatch in ATP supply and demand, contributing to poor prognosis. A link between Na_i and altered metabolism has been proposed but is not well understood. Many mitochondrial enzymes are stimulated by mitochondrial calcium (Ca_mito) during contraction, thereby sustaining production of reducing equivalents to maintain ATP supply. This stimulation is thought to be perturbed when cytosolic Na_i is high due to increased Ca_mito efflux, potentially compromising ATP_mito production and leading to metabolic dysregulation. Increased Na_i has been previously shown to affect Ca_mito; however, whether Na_i elevation plays a causative role in energetic mismatching in the hypertrophied and failing heart remains unknown. In this review, we discuss the relationship between elevated Na_i, NaK ATPase dysregulation and the metabolic phenotype in the contexts of pathological hypertrophy and HF and their link to metabolic flexibility, capacity (reserve) and efficiency that are governed by intracellular ion homeostasis. The development of non-invasive analytical techniques using nuclear magnetic resonance able to probe metabolism in situ in the functioning heart will enable a better understanding of the underlying mechanisms of Na_i overload in cardiac pathophysiology. They will lead to novel insights that help to explain the metabolic contribution towards these diseases, the incomplete rescue observed with current therapies and a rationale for future energy-targeted therapies.

AMPK in Cardiovascular Diseases

This chapter summarizes the implication of AMP-activated protein kinase (AMPK) in the regulation of various physiological and pathological cellular events of great importance for the maintenance of cardiac function. These include the control of both metabolic and non-metabolic elements targeting the different cellular components of the cardiac tissue, i.e., cardiomyocytes, fibroblasts, and vascular cells. The description of the multifaceted action of the two AMPK catalytic isoforms, α1 and α2, emphasizes the general protective action of this protein kinase against the development of critical pathologies like myocardial ischemia, cardiac hypertrophy, diabetic cardiomyopathy, and heart failure.

Comparison between myocardial infarction and diabetes mellitus damage caused angiogenesis or energy metabolism

This study aims to compare and analyze lactate dehydrogenase (LDH), succinic dehydrogenase (SDH) and differences in capillary density level in the model of myocardial damage which caused by rats diabetes. The Wistar rats were divided into 4 groups, including control, diabetic, myocardial infarction and two diseases combined group. Ligate descending branch of left coronary artery on 1/3 position or inject streptozotocin into abdominal cavity to establish two kinds of disease models. After 6 w, obtain the myocardial tissues to do the vascular density analysis of tissue sections which are stained and cell tissue enzyme. Explore change of relevant index and differences among groups. Results indicated that degree of LDH and SDH decrease in two kinds of disease model. Compared with control group, level of myocardial vascular of myocardial injury group is higher, and diabetic group is higher than non diabetic group. Quantitative result of FFA in mitochondrial suspension of single disease group is higher than that of control group and two diseases combined group. Level of FFA and LDH of two diseases combined group is consistent with control group. In conclusion, after myocardial damage, which is caused by diabetes mellitus or myocardial infarction, degree of local vascularization increases, diabetes mellitus is more obvious. After myocardial damage, process of myocardial mitochondrial glycolysis and oxidative phosphorylation has some obstacles. But these two kinds of diseases all have cardiac muscle cell which can keep generated procedure of aerobic and anaerobic energy to instead the normal function of cardiac muscle.

AMPK: energy sensor and survival mechanism in the ischemic heart

AMP-activated protein kinase (AMPK) is a critical regulator of cellular metabolism and plays an important role in diabetes, cancer, and vascular disease. In the heart, AMPK activation is an essential component of the adaptive response to cardiomyocyte stress that occurs during myocardial ischemia. During ischemia-reperfusion, AMPK activation modulates glucose and fatty acid metabolism, mitochondrial function, endoplasmic reticulum (ER) stress, autophagy, and apoptosis. Pharmacological activation of AMPK prevents myocardial necrosis and contractile dysfunction during ischemia-reperfusion and potentially represents a cardioprotective strategy for the treatment of myocardial infarction. This review discusses novel mechanisms of AMPK activation in the ischemic heart, the role of endogenous AMPK activation during ischemia, and the potential therapeutic applications for AMPK-directed therapy.

The effects of mitochondrial complex I blockade on ATP and permeability in rat pulmonary microvascular endothelial cells in culture (PMVEC) are overcome by coenzyme Q1 (CoQ1)

In isolated rat lung perfused with a physiological saline solution (5.5mM glucose), complex I inhibitors decrease lung tissue ATP and increase endothelial permeability (Kf), effects that are overcome using an amphipathic quinone (CoQ1) [Free Radic. Biol. Med.65:1455-1463; 2013]. To address the microvascular endothelial contribution to these intact lung responses, rat pulmonary microvascular endothelial cells in culture (PMVEC) were treated with the complex I inhibitor rotenone and ATP levels and cell monolayer permeability (PS) were measured. There were no detectable effects on ATP or permeability in experimental medium that, like the lung perfusate, contained 5.5mM glucose. To unmask a potential mitochondrial contribution, the glucose concentration was lowered to 0.2mM. Under these conditions, rotenone decreased ATP from 18.4±1.6 (mean±SEM) to 4.6±0.8nmol/mg protein, depolarized the mitochondrial membrane potential (Δψm) from -129.0±3.7 (mean±SEM) to -92.8±5.5mV, and decreased O2 consumption from 2.0±0.1 (mean±SEM) to 0.3±0.1nmol/min/mg protein. Rotenone also increased PMVEC monolayer permeability (reported as PS in nl/min) to FITC-dextran (~40kDa) continually over a 6 h time course. When CoQ1 was present with rotenone, normal ATP (17.4±1.4nmol/mg protein), O2 consumption (1.5±0.1nmol/min/mg protein), Δψm (-125.2±3.3mV), and permeability (PS) were maintained. Protective effects of CoQ1 on rotenone-induced changes in ATP, O2 consumption rate, Δψm, and permeability were blocked by dicumarol or antimycin A, inhibitors of the quinone-mediated cytosol-mitochondria electron shuttle [Free Radic. Biol. Med.65:1455-1463; 2013]. Key rotenone effects without and with CoQ1 were qualitatively reproduced using the alternative complex I inhibitor, piericidin A. We conclude that, as in the intact lung, PMVEC ATP supply is linked to the permeability response to complex I inhibitors. In contrast to the intact lung, the association in PMVEC was revealed only after decreasing the glucose concentration in the experimental medium from 5.5 to 0.2mM.

Dichloroacetate selectively improves cardiac function and metabolism in female and male rainbow trout

Cardiac tissue from female rainbow trout demonstrates a sex-specific preference for exogenous glucose and glycolysis, impaired Ca(2+) handling, and a greater tolerance for hypoxia and reoxygenation than cardiac tissue from male rainbow trout. We tested the hypothesis that dichloroacetate (DCA), an activator of pyruvate dehydrogenase, enhances cardiac energy metabolism and Ca(2+) handling in female preparations and provide cardioprotection for hypoxic male tissue. Ventricle strips from sexually immature fish with very low (male) and nondetectable (female) plasma sex steroids were electrically paced in oxygenated or hypoxic Ringer solution with or without 1 mM DCA. In the presence of 5 mM glucose, aerobic tissue from male trout could be paced at a higher frequency (1.79 vs. 1.36 Hz) with lower resting tension and less contractile dysfunction than female tissue. At 0.5 Hz, DCA selectively reduced resting tension below baseline values and lactate efflux by 75% in aerobic female ventricle strips. DCA improved the functional recovery of developed twitch force, reduced lactate efflux by 50%, and doubled citrate in male preparations after hypoxia-reoxygenation. Independent of female sex steroids, reduced myocardial pyruvate dehydrogenase activity and impaired carbohydrate oxidation might explain the higher lactate efflux, compromised function of the sarcoplasmic reticulum, and reduced mechanical performance of aerobic female tissue. Elevated oxidative metabolism and reduced glycolysis might also underlie the beneficial effects of DCA on the mechanical recovery of male cardiac tissue after hypoxia-reoxygenation. These results support the use of rainbow trout as an experimental model of sex differences of cardiovascular energetics and function, with the potential for modifying metabolic phenotypes and cardioprotection independent of sex steroids.

Non-preferential fuelling of the Na(+)/K(+)-ATPase pump

There is abundant evidence that glycolysis and the Na(+)/K(+)-ATPase pump are functionally coupled, and it is thought that the nature of the coupling is energetic, with glycolysis providing the ATP that fuels the pump. This notion has been instrumental to current models of brain energy metabolism. However, structural and biophysical considerations suggest that the pump should also have access to mitochondrial ATP, which is much more abundant. In the present study, we have investigated the source of ATP that fuels the Na(+) pump in astrocytes, taking advantage of the high temporal resolution of recently available FRET nanosensors for glucose, lactate and ATP. The activity of the Na(+) pump was assessed in parallel with the Na(+)-sensitive dye SBFI AM (Na(+)-binding benzofuran isophthalate acetoxymethyl ester). OXPHOS (oxidative phosphorylation) inhibition resulted in bulk ATP depletion and a 5-fold stimulation of glycolytic flux, in spite of which Na(+) pumping was inhibited by 90%. Mathematical modelling of ATP dynamics showed that the observed pump failure is inconsistent with preferential fuelling of the Na(+) pump by glycolytic ATP. We conclude that the nature of the functional coupling between the Na(+) pump and the glycolytic machinery is not energetic and that the pump is mainly fuelled by mitochondrial ATP.

Tight coupling of Na+/K+-ATPase with glycolysis demonstrated in permeabilized rat cardiomyocytes

The effective integrated organization of processes in cardiac cells is achieved, in part, by the functional compartmentation of energy transfer processes. Earlier, using permeabilized cardiomyocytes, we demonstrated the existence of tight coupling between some of cardiomyocyte ATPases and glycolysis in rat. In this work, we studied contribution of two membrane ATPases and whether they are coupled to glycolysis--sarcoplasmic reticulum Ca2+ ATPase (SERCA) and plasmalemma Na+/K+-ATPase (NKA). While SERCA activity was minor in this preparation in the absence of calcium, major role of NKA was revealed accounting to ∼30% of the total ATPase activity which demonstrates that permeabilized cell preparation can be used to study this pump. To elucidate the contribution of NKA in the pool of ATPases, a series of kinetic measurements was performed in cells where NKA had been inhibited by 2 mM ouabain. In these cells, we recorded: ADP- and ATP-kinetics of respiration, competition for ADP between mitochondria and pyruvate kinase (PK), ADP-kinetics of endogenous PK, and ATP-kinetics of total ATPases. The experimental data was analyzed using a series of mathematical models with varying compartmentation levels. The results show that NKA is tightly coupled to glycolysis with undetectable flux of ATP between mitochondria and NKA. Such tight coupling of NKA to PK is in line with its increased importance in the pathological states of the heart when the substrate preference shifts to glucose.

The impact of obesity and hypoxia on left ventricular function and glycolytic metabolism

We have previously reported that 4 weeks of intermittent hypoxia (IH) exposure, mimicking the hypoxic stress of obstructive sleep apnea, produces compensatory increases in left ventricular (LV) contractility in lean C57BL/6J mice. In this study we compared the effects of 4 weeks IH to 4 weeks of sustained hypoxia (SH) on LV function and cardiac glycolysis in lean C57BL/6J mice and obese ob/ob mice at 10–12 weeks of age. The four exposure conditions were IH (nadir O₂ [5–6%] at 60 cycles/h during the 12 h light period), SH (24 h inspired O₂ [10%]), and control groups of intermittent air (IA) or room air. Cardiac function was assessed under isoflurane anesthesia (1–2%) by echocardiography and pressure–volume loop analysis and myocardial glycolytic rates were determined ex vivo using radiolabeled ³H‐glucose. Lean mice exposed to IH exhibited increases in contractile parameters which were associated with elevated glycolytic rates (3.4 vs. 5.7 μg/μL·g; P < 0.05). Ob/ob mice did not show any improvements in contractility after IH. Moreover, cardiac glycolytic rates and LV systolic and diastolic function did not differ from IA ob/ob controls. Following SH exposure, lean mice exhibited increased contractility and glycolytic rates (3.8 vs. 5.7 μg/μL·g; P < 0.05), however, LV lumen dimensions were reduced. In contrast, ob/ob mice exposed to SH show compromised systolic and diastolic function associated with unchanging glycolytic rates. These findings demonstrate that, in a murine model of obesity, an inability to increase glycolysis is associated with an absence of an adaptive cardiac response to IH and marked systolic and diastolic dysfunction in response to SH.

The impact of obesity on left ventricular (LV) function and cardiac glycolytic responses to chronic 4 week exposure to intermittent hypoxia, mimicking the hypoxic stress of obstructive sleep apnea, or sustained hypoxia, mimicking altitude exposure, is unknown. We show that, in a murine model of obesity, an inability to increase glycolysis is associated with an absence of an adaptive cardiac response to intermittent hypoxia and marked systolic and diastolic dysfunction in response to sustained hypoxia.

Comparative analysis of changes of myocardial angiogenesis and energy metabolism in postinfarction and diabetic damage of rat heart

Comparative study of changes in myocardial activity of lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), and capillary density distribution in the experimental models of diabetic and postinfarction damage of rat heart was performed. Data showed that decrease in LDH and SDH activities was observed in both pathologies which can suggest abnormal processes of glycolysis and oxidative phosphorylation in cardiac mitochondria. Activity of LDH and SDH in combined pathologies was comparative with the corresponding values of these parameters in control group. The authors hypothesize that these differences can be caused by specifics of myocardial vascularization. The results of the study showed that an increase in capillary density was found in all groups of rats with pathologies compared with control group. However, no significant differences in the intensity of angiogenesis processes were found between groups with pathologies.

Continuous inhibition of poly(ADP-ribose) polymerase does not reduce reperfusion injury in isolated rat heart

Poly(ADP-ribose) polymerase (PARP), an enzyme that is important to the regulation of nuclear function, is activated by DNA strand breakage. In massive DNA damage, PARP is overactivated, exhausting nicotinamide adenine dinucleotide and leading to cell death. Recent studies have succeeded in reducing cellular damage in ischemia/reperfusion by inhibiting PARP. However, PARP plays an important part in the DNA repair system, and its inhibition may be hazardous in certain situations. We compared the short-time inhibition of PARP against continuous inhibition during ischemia/reperfusion using isolated rat hearts. The hearts were reperfused after 21 minutes of ischemia with a bolus injection of 3-aminobenzamide (3-AB) (10 mg/kg) followed by continuous 3-AB infusion (50 μM) for the whole reperfusion period or for the first 6 minutes or without 3-AB. At the end of reperfusion, contractile function, high-energy phosphate content, nicotinamide adenine dinucleotide content, and infarcted area were significantly preserved in the 3-AB 6-minute group. In the 3-AB continuous group, these advantages were not apparent. At the end of reperfusion, PARP cleavage had significantly proceeded in the 3-AB continuous group, indicating initiation of the apoptotic cascade. Thus, continuous PARP inhibition by 3-AB does not reduce reperfusion injury in the isolated rat heart, which may be because of acceleration of apoptosis.

Compartmentation of GAPDH

The concept of the cytosol as a space that contains discrete zones of metabolites is discussed relative to the contribution of GAPDH. GAPDH is directed to very specific cell compartments. This chapter describes the utilization of GAPDH's enzymatic function for focal demands (i.e. ATP/ADP and NAD(+)/NADH), and offers a speculative role for GAPDH as perhaps moderating local concentrations of inorganic phosphate and hydrogen ions (i.e. co-substrate and co-product of the glycolytic reaction, respectively). Where known, the structural features of the binding between GAPDH and the compartment components are discussed. The nuances, which are associated with the intracellular distribution of GAPDH, appear to be specific to the cell-type, particularly with regards to the various plasma membrane proteins to which GAPDH binds. The chapter includes discussion on the curious observation of GAPDH being localized to the external surface of the plasma membrane in a human cell type. The default perspective has been that GAPDH localization is synonymous with compartmentation of glycolytic energy. The chapter discusses GAPDH translocation to the nucleus and to non-nuclear cellular structures, emphasizing its glycolytic function. Nevertheless, it is becoming clear that alternate functions of GAPDH play a role in compartmentation, particularly in the translocation to the nucleus.

Compartmentation of membrane processes and nucleotide dynamics in diffusion-restricted cardiac cell microenvironment

Orchestrated excitation-contraction coupling in heart muscle requires adequate spatial arrangement of systems responsible for ion movement and metabolite turnover. Co-localization of regulatory and transporting proteins into macromolecular complexes within an environment of microanatomical cell components raises intracellular diffusion barriers that hamper the mobility of metabolites and signaling molecules. Compared to substrate diffusion in the cytosol, diffusional restrictions underneath the sarcolemma are much larger and could impede ion and nucleotide movement by a factor of 10(3)-10(5). Diffusion barriers thus seclude metabolites within the submembrane space enabling rapid and vectorial effector targeting, yet hinder energy supply from the bulk cytosolic space implicating the necessity for a shunting transfer mechanism. Here, we address principles of membrane protein compartmentation, phosphotransfer enzyme-facilitated interdomain energy transfer, and nucleotide signal dynamics at the subsarcolemma-cytosol interface. This article is part of a Special Issue entitled "Local Signaling in Myocytes".

Molecular system bioenergics of the heart: experimental studies of metabolic compartmentation and energy fluxes versus computer modeling

In this review we analyze the recent important and remarkable advancements in studies of compartmentation of adenine nucleotides in muscle cells due to their binding to macromolecular complexes and cellular structures, which results in non-equilibrium steady state of the creatine kinase reaction. We discuss the problems of measuring the energy fluxes between different cellular compartments and their simulation by using different computer models. Energy flux determinations by ¹⁸O transfer method have shown that in heart about 80% of energy is carried out of mitochondrial intermembrane space into cytoplasm by phosphocreatine fluxes generated by mitochondrial creatine kinase from adenosine triphosphate (ATP), produced by ATP Synthasome. We have applied the mathematical model of compartmentalized energy transfer for analysis of experimental data on the dependence of oxygen consumption rate on heart workload in isolated working heart reported by Williamson et al. The analysis of these data show that even at the maximal workloads and respiration rates, equal to 174 μmol O₂ per min per g dry weight, phosphocreatine flux, and not ATP, carries about 80–85% percent of energy needed out of mitochondria into the cytosol. We analyze also the reasons of failures of several computer models published in the literature to correctly describe the experimental data.

A computational model of cytosolic and mitochondrial [ca] in paced rat ventricular myocytes

We carried out a series of experiment demonstrating the role of mitochondria in the cytosolic and mitochondrial Ca(2+) transients and compared the results with those from computer simulation. In rat ventricular myocytes, increasing the rate of stimulation (1~3 Hz) made both the diastolic and systolic [Ca(2+)] bigger in mitochondria as well as in cytosol. As L-type Ca(2+) channel has key influence on the amplitude of Ca(2+)-induced Ca(2+) release, the relation between stimulus frequency and the amplitude of Ca(2+) transients was examined under the low density (1/10 of control) of L-type Ca(2+) channel in model simulation, where the relation was reversed. In experiment, block of Ca(2+) uniporter on mitochondrial inner membrane significantly reduced the amplitude of mitochondrial Ca(2+) transients, while it failed to affect the cytosolic Ca(2+) transients. In computer simulation, the amplitude of cytosolic Ca(2+) transients was not affected by removal of Ca(2+) uniporter. The application of carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP) known as a protonophore on mitochondrial membrane to rat ventricular myocytes gradually increased the diastolic [Ca(2+)] in cytosol and eventually abolished the Ca(2+) transients, which was similarly reproduced in computer simulation. The model study suggests that the relative contribution of L-type Ca(2+) channel to total transsarcolemmal Ca(2+) flux could determine whether the cytosolic Ca(2+) transients become bigger or smaller with higher stimulus frequency. The present study also suggests that cytosolic Ca(2+) affects mitochondrial Ca(2+) in a beat-to-beat manner, however, removal of Ca(2+) influx mechanism into mitochondria does not affect the amplitude of cytosolic Ca(2+) transients.

What is the risk of hyperkalaemia in heart failure?

INTRODUCTION

Chronic heart failure (CHF) is the only major cardiovascular disease whose prevalence and incidence are thought to be increasing. Potassium balance may be lost both through the neurohormonal mechanisms involved in cardiovascular diseases and through the drugs used in their treatment. Avoiding both hypo- and hyperkalemia is difficult but beneficial in CHF.

AREAS COVERED

Aldosterone production is decreased in the elderly, diabetic patients, and those receiving drugs that block the production or action of renin and angiotensin II. As a result, these groups, as well as those with already impaired potassium excretion due to progressive age or disease-related decline in glomerular filtration rate, are particularly vulnerable to the development of hyperkalemia.

EXPERT OPINION

Evidence from several studies suggests that, in patients with CHF, serum potassium should be maintained between 4.0 and 5.5 mEq/L. To gain the maximum benefit from aldosterone antagonists it is necessary to individualize their use; it is also necessary to carefully monitor electrolytes.

Effects of high-dose insulin infusion on left ventricular function in normal subjects

Background. Only a few studies have reported on the effect of high-dose insulin (HDI) infusion on cardiac function in healthy volunteers. Methods. We studied ten healthy volunteers with low-dose dobutamine (LDD, 10 mug/kg/min) echo-cardio-graphy and HDI echocardiography (insulin administration for one hour) by volume and Doppler analysis. Results. During LDD, cardiac output increased from 5.7+/-1.3 l/min to 9.0+/-2.1 l/min (p<0.001) and during HDI from 5.5+/-1.2 l/min to 6.2+/-1.1 l/min (p=0.048). Increase was not only due to increase in frequency, which was only present in the LDD study, but also due to increase in stroke volume (from 82+/-15 ml to 110+/-23 ml, p<0.001 during LDD and from 82+/-16 ml to 93+/-24 ml, p=0.014 during HDI). The increase in stroke volume was the result of a decrease in end-systolic volume with an unchanged end-diastolic volume. Conclusion. High-dose insulin infusion results in increased cardiac output by improving systolic myocardial function. (Neth Heart J 2010;18:183-9.).

Glycolytic inhibition causes spontaneous ventricular fibrillation in aged hearts

Selective glycolytic inhibition (GI) promotes electromechanical alternans and triggered beats in isolated cardiac myocytes. We sought to determine whether GI promotes triggered activity by early afterdepolarization (EAD) or delayed afterdepolarizations in intact hearts isolated from adult and aged rats. Dual voltage and intracellular calcium ion (Ca(i)(2+)) fluorescent optical maps and single cell glass microelectrode recordings were made from the left ventricular (LV) epicardium of isolated Langendorff-perfused adult (∼4 mo) and aged (∼24 mo) rat hearts. GI was induced by replacing glucose with 10 mM pyruvate in oxygenated Tyrode's. Within 20 min, GI slowed Ca(i)(2+) transient decline rate and shortened action potential duration in both groups. These changes were associated with ventricular fibrillation (VF) in the aged hearts (64 out of 66) but not in adult hearts (0 out of 18; P < 0.001). VF was preceded by a transient period of focal ventricular tachycardia caused by EAD-mediated triggered activity leading to VF within seconds. The VF was suppressed by the ATP-sensitive K (K(ATP)) channel blocker glibenclamide (1 μM) but not (0 out of 7) by mitochondrial K(ATP) block. The Ca-calmodulin-dependent protein kinase II (CaMKII) blocker KN-93 (1 μM) prevented GI-mediated VF (P < 0.05). Block of Na-Ca exchanger (NCX) by SEA0400 (2 μM) prevented GI-mediated VF (3 out of 6), provided significant bradycardia did not occur. Aged hearts had significantly greater LV fibrosis and reduced connexin 43 than adult hearts (P < 0.05). We conclude that in aged fibrotic unlike in adult rat hearts, GI promotes EADs, triggered activity, and VF by activation of K(ATP) channels CaMKII and NCX.

K(ATP) channels process nucleotide signals in muscle thermogenic response

Uniquely gated by intracellular adenine nucleotides, sarcolemmal ATP-sensitive K(+) (K(ATP)) channels have been typically assigned to protective cellular responses under severe energy insults. More recently, K(ATP) channels have been instituted in the continuous control of muscle energy expenditure under non-stressed, physiological states. These advances raised the question of how K(ATP) channels can process trends in cellular energetics within a milieu where each metabolic system is set to buffer nucleotide pools. Unveiling the mechanistic basis of the K(ATP) channel-driven thermogenic response in muscles thus invites the concepts of intracellular compartmentalization of energy and proteins, along with nucleotide signaling over diffusion barriers. Furthermore, it requires gaining insight into the properties of reversibility of intrinsic ATPase activity associated with K(ATP) channel complexes. Notwithstanding the operational paradigm, the homeostatic role of sarcolemmal K(ATP) channels can be now broadened to a wider range of environmental cues affecting metabolic well-being. In this way, under conditions of energy deficit such as ischemic insult or adrenergic stress, the operation of K(ATP) channel complexes would result in protective energy saving, safeguarding muscle performance and integrity. Under energy surplus, downregulation of K(ATP) channel function may find potential implications in conditions of energy imbalance linked to obesity, cold intolerance and associated metabolic disorders.

Lysophosphatidic acid receptor activation affects the C13NJ microglia cell line proteome leading to alterations in glycolysis, motility, and cytoskeletal architecture

Microglia, the immunocompetent cells of the CNS, are rapidly activated in response to injury and microglia migration towards and homing at damaged tissue plays a key role in CNS regeneration. Lysophosphatidic acid (LPA) is involved in signaling events evoking microglia responses through cognate G protein-coupled receptors. Here we show that human immortalized C13NJ microglia express LPA receptor subtypes LPA(1), LPA(2), and LPA(3) on mRNA and protein level. LPA activation of C13NJ cells induced Rho and extracellular signal-regulated kinase activation and enhanced cellular ATP production. In addition, LPA induced process retraction, cell spreading, led to pronounced changes of the actin cytoskeleton and reduced cell motility, which could be reversed by inhibition of Rho activity. To get an indication about LPA-induced global alterations in protein expression patterns a 2-D DIGE/LC-ESI-MS proteomic approach was applied. On the proteome level the most prominent changes in response to LPA were observed for glycolytic enzymes and proteins regulating cell motility and/or cytoskeletal dynamics. The present findings suggest that naturally occurring LPA is a potent regulator of microglia biology. This might be of particular relevance in the pathophysiological context of neurodegenerative disorders where LPA concentrations can be significantly elevated in the CNS.

Low carbohydrate diet decreases myocardial insulin signaling and increases susceptibility to myocardial ischemia

AIMS

Low Carbohydrate Diets (LCD) are a popular intervention for weight loss, but the effect of such diets on myocardial ischemia is not known. Myocardial energy substrates and insulin signaling pathways may be affected by these diets, and both may play a role in protection of ischemic myocardium. We investigated whether LCD increases susceptibility to cardiac injury during ischemia and reperfusion in the isolated rat heart.

MAIN METHODS

Rats were fed LCD (60% kcal from fat/30% protein/10% carbohydrate) or a control diet (CONT; 16%/19%/65%) for 2 weeks. Hearts from rats fed with LCD or CONT were isolated and subjected to normal perfusion in Langendorff mode, with 30 min global low flow ischemia (LFI; 0.3 ml/min) followed by 60 min reperfusion, or 60 min LFI followed by 120 min reperfusion.

KEY FINDINGS

LCD diet led to an increase in 3-hydroxybutyrate and lower circulating insulin. LCD diet also resulted in impaired left ventricular performance during LFI, reduced recovery of function following LFI and reperfusion, and 10- to 20-fold increased injury as measured by lactate dehydrogenase release and histologic infarct area. LCD diet also led to lower myocardial glycogen stores and glycogen utilization during LFI, and lower insulin signaling as assessed by Akt phosphorylation at the end of LFI and reperfusion, but no differences in ERK 1/2 phosphorylation.

SIGNIFICANCE

These results demonstrate that LCD affects myocardial energy substrates, affects insulin signaling, and increases myocardial injury following ischemia-reperfusion in the isolated heart.

Impact of anaerobic glycolysis and oxidative substrate selection on contractile function and mechanical efficiency during moderate severity ischemia

The role of anaerobic glycolysis and oxidative substrate selection on contractile function and mechanical efficiency during moderate severity myocardial ischemia is unclear. We hypothesize that 1) preventing anaerobic glycolysis worsens contractile function and mechanical efficiency and 2) increasing glycolysis and glucose oxidation while inhibiting free fatty acid oxidation improves contractile function during ischemia. Experiments were performed in anesthetized pigs, with regional ischemia induced by a 60% decrease in left anterior descending coronary artery blood flow for 40 min. Three groups were studied: 1) no treatment, 2) inhibition of glycolysis with iodoacetate (IAA), or 3) hyperinsulinemia and hyperglycemia (HI + HG). Glucose and free fatty acid oxidation were measured using radioisotopes and anaerobic glycolysis from net lactate efflux and myocardial lactate content. Regional contractile power was assessed from left ventricular pressure and segment length in the anterior wall. We found that preventing anaerobic glycolysis with IAA during ischemia in the absence of alterations in free fatty acid and glucose oxidation did not adversely affect contractile function or mechanical efficiency during myocardial ischemia, suggesting that anaerobic glycolysis is not essential for maintaining residual contractile function. Increasing glycolysis and glucose oxidation with HI + HG inhibited free fatty acid oxidation and improved contractile function and mechanical efficiency. In conclusion, these results show a dissociation between myocardial function and anaerobic glycolysis during moderate severity ischemia in vivo, suggesting that metabolic therapies should not be aimed at inhibiting anaerobic glycolysis per se, but rather activating insulin signaling and/or enhancing carbohydrate oxidation and/or decreasing fatty acid oxidation.

Effects of metabolic inhibition on conduction, Ca transients, and arrhythmia vulnerability in embryonic mouse hearts

Developing myocardium is more dependent on glycolysis than adult myocardium, yet the effects of selectively inhibiting glycolysis versus oxidative phosphorylation on embryonic heart function have not been well characterized. Accordingly, we investigated how selective metabolic inhibition affects membrane voltage and intracellular Ca (Ca(i)) transients in embryonic mouse hearts, including their susceptibility to arrhythmias. A total of 136 isolated embryonic mouse hearts were exposed to either 1) 2-deoxyglucose (2DG; 10 mM) or iodoacetate (IAA; 0.1 mM) with 10 mM pyruvate in place of glucose to selectively inhibit glycolysis or 2) the mitochondrial uncoupler protonophore carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (FCCP; 500 nM) with 10 mM glucose present to selectively inhibit oxidative phosphorylation. Using confocal imaging, we found that mitochondrial membrane potential monitored with tetramethylrhodamine methyl ester (200 nM) remained stable with 2DG or IAA but depolarized within 5 min after exposure to FCCP. IAA and FCCP decreased heart rate, inhibited Ca(i) transient amplitude, shortened action potential duration at 80% repolarization (APD(80)), and prolonged atrioventricular conduction time to similar extents. Although 2DG decreased heart rate and Ca(i) transient amplitude, it did not significantly affect APD(80) and AV conduction time. In addition, spontaneous arrhythmias occurred in 77 of 136 embryonic hearts (57%) after exposure to IAA (28/53) or FCCP (49/83). There were no significant differences in the types or incidence of arrhythmias induced by IAA and FCCP. These data support the idea that both glycolysis and oxidative phosphorylation play critical metabolic roles in regulating cardiac function in the embryonic mouse heart.

An enquiry into metabolite domains

It is currently assumed that two or more pools of the same metabolite can coexist in the cytosolic compartment of mammalian cells. These pools are thought to be generated by the differential subcellular location of enzymes and transporters, much in the way calcium microdomains arise by the combined workings of channels, buffers, and pumps. With the aim of estimating the amplitude and spatial dimensions of these metabolite pools, we developed an analytical tool based on Brownian diffusion and the turnover numbers of the proteins involved. The outcome of the analysis is that ATP, glucose, pyruvate, lactate, and glutamate cannot be concentrated at their sources to an extent that would affect their downstream targets. For these metabolites, and others produced by slow enzymes or transporters and present at micromolar concentrations or higher, the cytosol behaves as a well-mixed, homogenous compartment. In contrast, the analysis showed microdomains known to be generated by calcium channels and revealed that calcium and pH nanodomains are to be found in the vicinity of slow enzymes and transporters in the steady state. The analysis can be readily applied to any other molecule, provided knowledge is available about rate of production, average concentration, and diffusion coefficient. Our main conclusion is that the notion of cytosolic compartmentation of metabolites needs reevaluation, as it seems to be in conflict with the underlying physical chemistry.

Role of glycolytically generated ATP for CaMKII-mediated regulation of intracellular Ca2+ signaling in bovine vascular endothelial cells

The role of glycolytically generated ATP in Ca(2+)/calmodulin-dependent kinase II (CaMKII)-mediated regulation of intracellular Ca(2+) signaling was examined in cultured calf pulmonary artery endothelial (CPAE) cells. Exposure of cells (extracellular Ca(2+) concentration = 2 mM) to glycolytic inhibitors 2-deoxy-D-glucose (2-DG), pyruvate (pyr) + beta-hydroxybutyrate (beta-HB), or iodoacetic acid (IAA) caused an increase of intracellular Ca(2+) concentration ([Ca(2+)](i)). CaMKII inhibitors (KN-93, W-7) triggered a similar increase of [Ca(2+)](i). The rise of [Ca(2+)](i) was characterized by a transient spike followed by a small sustained plateau of elevated [Ca(2+)](i). In the absence of extracellular Ca(2+) 2-DG caused an increase in [Ca(2+)](i), suggesting that inhibition of glycolysis directly triggered release of Ca(2+) from intracellular endoplasmic reticulum (ER) Ca(2+) stores. The inositol-1,4,5-trisphosphate receptor (IP(3)R) inhibitor 2-aminoethoxydiphenyl borate abolished the KN-93- and 2-DG-induced Ca(2+) response. Ca(2+) release was initiated in peripheral cytoplasmic processes from which activation propagated as a [Ca(2+)](i) wave toward the central region of the cell. Focal application of 2-DG resulted in spatially confined elevations of [Ca(2+)](i). Propagating [Ca(2+)](i) waves were preceded by [Ca(2+)](i) oscillations and small, highly localized elevations of [Ca(2+)](i) (Ca(2+) puffs). Inhibition of glycolysis with 2-DG reduced the KN-93-induced Ca(2+) response, and vice versa during inhibition of CaMKII 2-DG-induced Ca(2+) release was attenuated. Similar results were obtained with pyr + beta-HB and W-7. Furthermore, 2-DG and IAA caused a rapid increase of intracellular Mg(2+) concentration, indicating a concomitant drop of cellular ATP levels. In conclusion, CaMKII exerts a profound inhibition of ER Ca(2+) release in CPAE cells, which is mediated by glycolytically generated ATP, possibly through ATP-dependent phosphorylation of the IP(3)R.

Annexin-I as a potential target for green tea extract induced actin remodeling

Using a multistep human urothelial model, we previously showed that green tea extract (GTE) selectively modulates actin remodeling in transformed cells (MC-T11), which resulted in increased cell adhesion and reduced cell motility (Lu et al., Clin Cancer Res 2005;11:1675-83). This study further analyzed which actin binding proteins (ABPs) might be involved in this process. Proteomic profiles of GTE treated and untreated MC-T11 cells using two-dimensional gel electrophoresis coupled with liquid chromatography tandem mass spectrometry (LC/MS/MS) and matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) identified 20 GTE-induced proteins. Among them, 3 were ABPs (tropomodulin, cofilin and annexin-I), and only annexin-I showed a dose- and time-dependent expression. The increased annexin-I correlated with actin remodeling, and was the result of transcription level up-regulation, as determined by RT-PCR, pull-down immunoblot and siRNA analyses. 5-Azacytidine, a DNA methylation inhibitor, exhibited no effect on annexin-I expression when used alone, but had an additive effect for GTE-induced annexin-I expression. Immunohistochemistry of bladder cancer tissue array showed a decrease of annexin-I expression in carcinoma in situ and low grade papillary carcinoma (n = 32, 0% positive) compared to nontumor urothelium (n = 18, 89% positive) (p < 0.001 by Fisher exact test), but increased in some (6 of 15, 40%) high-grade tumors. Together, GTE induced annexin-I expression plays a role in regulating actin remodeling and decreased annexin-I expression is a common event in early stage of bladder cancer development.

Causes and characteristics of diabetic cardiomyopathy

Type 1 and type 2 diabetic patients are at increased risk of cardiomyopathy and heart failure is a major cause of death for these patients. Cardiomyopathy in diabetes is associated with a cluster of features including decreased diastolic compliance, interstitial fibrosis and myocyte hypertrophy. The mechanisms leading to diabetic cardiomyopathy remain uncertain. Diabetes is associated with most known risk factors for cardiac failure seen in the overall population, including obesity, dyslipidemia, thrombosis, infarction, hypertension, activation of multiple hormone and cytokine systems, autonomic neuropathy, endothelial dysfunction and coronary artery disease. In light of these common contributing pathologies it remains uncertain whether diabetic cardiomyopathy is a distinct disease. It is also uncertain which factors are most important to the overall incidence of heart failure in diabetic patients. This review focuses on factors that can have direct effects on diabetic cardiomyocytes: hyperglycemia, altered fuel use, and changes in the activity of insulin and angiotensin. Particular attention is given to the changes these factors can have on cardiac mitochondria and the role of reactive oxygen species in mediating injury to cardiomyocytes.

Thematic review series: Systems Biology Approaches to Metabolic and Cardiovascular Disorders. Network perspectives of cardiovascular metabolism

In this review, we examine cardiovascular metabolism from three different, but highly complementary, perspectives. First, from the abstract perspective of a metabolite network, composed of nodes and links. We present fundamental concepts in network theory, including emergence, to illustrate how nature has designed metabolism with a hierarchal modular scale-free topology to provide a robust system of energy delivery. Second, from the physical perspective of a modular spatially compartmentalized network. We review evidence that cardiovascular metabolism is functionally compartmentalized, such that oxidative phosphorylation, glycolysis, and glycogenolysis preferentially channel ATP to ATPases in different cellular compartments, using creatine kinase and adenylate kinase to maximize efficient energy delivery. Third, from the dynamics perspective, as a network of dynamically interactive metabolic modules capable of self-oscillation. Whereas normally, cardiac metabolism exists in a regime in which excitation-metabolism coupling closely matches energy supply and demand, we describe how under stressful conditions, the network can be pushed into a qualitatively new dynamic regime, manifested as cell-wide oscillations in ATP levels, in which the coordination between energy supply and demand is lost. We speculate how this state of "metabolic fibrillation" leads to cell death if not corrected and discuss the implications for cardioprotection.

High dietary sucrose triggers hyperinsulinemia, increases myocardial β-oxidation, reduces glycolytic flux and delays post-ischemic contractile recovery

Although the causal relationship between insulin resistance (IR) and hypertension is not fully resolved, the importance of IR in cardiovascular dysfunction is recognized. As IR may follow excess sucrose or fructose diet, the aim of this study was to test whether dietary starch substitution with sucrose results in myocardial dysfunction in energy substrate utilization and contractility during normoxic and post-ischemic conditions. Forty-eight male Wistar rats were randomly allocated to three diets, differing only in their starch to sucrose (S) ratio (13, 2 and 0 for the Low S, Middle S and High S groups, respectively), for 3 weeks. Developed pressure and rate x pressure product (RPP) were determined in Langendorff mode-perfused hearts. After 30 min stabilization, hearts were subjected to 25 min of total normothermic global ischemia, followed by 45-min reperfusion. Oxygen consumption, beta-oxidation rate (using 1-13C hexanoate and Isotopic Ratio Mass Spectrometry of CO2 produced in the coronary effluent) and flux of non-oxidative glycolysis were also evaluated. Although fasting plasma glucose levels were not affected by increased dietary sucrose, high sucrose intake resulted in increased plasma insulin levels, without significant rise in plasma triglyceride and free fatty acid concentrations. Sucrose-rich diet reduced pre-ischemic baseline measures of heart rate, RPP and non-oxidative glycolysis. During reperfusion, post-ischemic recovery of RPP was impaired in the Middle S and High S groups, as compared to Low S, mainly due to delayed recovery of developed pressure, which by 45 min of reperfusion eventually resumed levels matching Low S. At the start of reperfusion, delayed post-ischemic recovery of contractile function was accompanied by: (i) reduced lactate production; (ii) decreased lactate to pyruvate ratio; (iii) increased beta-oxidation; and (iv) depressed metabolic efficiency. In conclusion, sucrose rich-diet increased plasma insulin levels, in intact rat, and increased cardiac beta-oxidation and coronary flow-rate, but reduced glycolytic flux and contractility during normoxic baseline function of isolated perfused hearts. Sucrose rich-diet impaired early post-ischemic recovery of isolated heart cardiac mechanical function and further augmented cardiac beta-oxidation but reduced glycolytic and lactate flux.

Similarities between ischemic preconditioning and 17beta-estradiol mediated cardiomyocyte KATP channel activation leading to cardioprotective and antiarrhythmic effects during ischemia/reperfusion in the intact rabbit heart

The aims of our present work were to assess whether treatment with either ischemic preconditioning (IPC) or 17beta-estradiol or both combined produce proarrhythmic or antiarrhythmic effects, and whether opening of the sarcolemmal or mitochondrial KATP channels is relatable to this effect; to assess biochemically the effects of IPC and/or 17beta-estradiol on oxidant stress and antioxidant defenses in the myocardium; to examine the effects of nitric oxide (NO) synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) pretreatment in rabbits treated with either IPC or 17beta-estradiol (because 17beta-estradiol evoked NO release has been implicated in KATP activation and IPC); and examine the effects of ischemic preconditioning and 17beta-estradiol on myocardial energy metabolism during ischemia and reperfusion in a well-standardized model of reperfusion arrhythmias in anesthetized adult male New Zealand White rabbits (n = 124) subjected to 30 minutes occlusion of the left coronary artery followed by 120 minutes of reperfusion. Pretreatment with either 17beta-estradiol (10 microg/kg, i.v.) or one cycle of ischemic preconditioning prior to the period of coronary occlusion offers significant infarct size reduction (18.6 +/- 2.2% and 19.4 +/- 1.9%, respectively versus 40.1 +/- 3.9% in saline control and 39.2 +/- 3.2% in vehicle control groups; P < 0.01) and antiarrhythmic effects. Both 17beta-estradiol and ischemic preconditioning treatment significantly attenuated the incidence of life-threatening arrhythmias like sustained VT (13% and 13%, respectively versus 100% in saline control and 100% in vehicle control groups; P < 0.001) and other arrhythmias (25% and 25%, respectively versus 100% in saline control and 100% in vehicle control groups; P < 0.001), and were quite effective in increasing the number of animals that survived without developing any arrhythmia during ischemia and reperfusion. 5-hydroxydecanoate(5-HD; 5 mg/kg, i.v.) alone offered no cardioprotective and antiarrhythmic activities. Pretreatment with 5-HD but not HMR 1883 (3 mg/kg, i.v.) abolished the beneficial effects of 17beta-estradiol and ischemia preconditioning on reperfusion-induced arrhythmias and cardioprotection suggesting that such effects have been achieved via the selective activation of cardiomyocyte mitochondrial KATP channels rather than sarcolemmal KATP channels. The reduced reperfusion arrhythmic incidence and durations induced by estrogen was not significantly altered by ICI 182 720 (2.5 mg/kg, i.v.). The lack of effect of ICI 182 720 on antiarrhythmic and infarct-limiting effects of 17beta-estradiol and ischemic preconditioning suggest that these favorable effects are rapid, direct, and non-genomic effects. This study demonstrates similarities between 17beta-estradiol and ischemic preconditioning of the rabbit myocardium in terms of cardioprotection, antiarrhythmic, and metabolic activities. Ischemic preconditioning and 17beta-estradiol appear to share a final common effector; the mitochondrial KATP channel.

Role of changes in cardiac metabolism in development of diabetic cardiomyopathy

In patients with diabetes, an increased risk of symptomatic heart failure usually develops in the presence of hypertension or ischemic heart disease. However, a predisposition to heart failure might also reflect the effects of underlying abnormalities in diastolic function that can occur in asymptomatic patients with diabetes alone (termed diabetic cardiomyopathy). Evidence of cardiomyopathy has also been demonstrated in animal models of both Type 1 (streptozotocin-induced diabetes) and Type 2 diabetes (Zucker diabetic fatty rats and ob/ob or db/db mice). During insulin resistance or diabetes, the heart rapidly modifies its energy metabolism, resulting in augmented fatty acid and decreased glucose consumption. Accumulating evidence suggests that this alteration of cardiac metabolism plays an important role in the development of cardiomyopathy. Hence, a better understanding of this dysregulation in cardiac substrate utilization during insulin resistance and diabetes could provide information as to potential targets for the treatment of cardiomyopathy. This review is focused on evaluating the acute and chronic regulation and dysregulation of cardiac metabolism in normal and insulin-resistant/diabetic hearts and how these changes could contribute toward the development of cardiomyopathy.

Measurement of activation energy and oxidative phosphorylation onset kinetics in isolated muscle fibers in the absence of cross-bridge cycling

This study utilized N-benzyl-p-toluene sulfonamide (BTS), a potent inhibitor of cross-bridge cycling, to measure 1) the relative metabolic costs of cross-bridge cycling and activation energy during contraction, and 2) oxygen uptake kinetics in the presence and absence of myosin ATPase activity, in isolated Xenopus laevis muscle fibers. Isometric tension development and either cytosolic Ca2+ concentration ([Ca2+]c) or intracellular Po2 (PiO2) were measured during contractions at 20 degrees C in control conditions (Con) and after exposure to 12.5 microM BTS. BTS attenuated tension development to 5+/-0.4% of Con but did not affect either resting or peak [Ca2+]c during repeated isometric contractions. To determine the relative metabolic cost of cross-bridge cycling, we measured the fall in PiO2) (DeltaPiO2; a proxy for Vo2) during contractions in Con and BTS groups. BTS attenuated DeltaP(iO2) by 55+/-6%, reflecting the relative ATP cost of cross-bridge cycling. Thus, extrapolating DeltaPiO2 to a value that would occur at 0% tension suggests that actomyosin ATP requirement is approximately 58% of overall ATP consumption during isometric contractions in mixed fiber types. BTS also slowed the fall in PiO2) (time to 63% of overall DeltaPiO2) from 75+/-9 s (Con) to 101+/-9 s (BTS) (P<0.05), suggesting an important role of the products of ATP hydrolysis in determining the Vo2 onset kinetics. These results demonstrate in isolated skeletal muscle fibers that 1) activation energy accounts for a substantial proportion (approximately 42%) of total ATP cost during isometric contractions, and 2) despite unchanged [Ca2+]c transients, a reduced rate of ATP consumption results in slower Vo2 onset kinetics.

Effect of exogenous adenosine and monensin on glycolytic flux in isolated perfused normoxic rat hearts: role of pyruvate kinase

We studied the effect of exogenous adenosine in isolated perfused normoxic rat hearts on glycolytic flux through pyruvate kinase (PK). We compared its effect with that of myxothiazol, an inhibitor of mitochondrial ATP production. Moreover, we tested whether an increase of membrane ionic flux with monensin is linked to a stimulation of glycolytic flux through PK. After a 20-min stabilization period adenosine, myxothiazol or monensin were administrated to the perfusate continuously at various concentrations during 10 min. The contraction was monitored and the lactate production in coronary effluents evaluated. The amount of adenine nucleotides and phosphoenolpyruvate was measured in the frozen hearts. Myxothiazol induced a decrease of the left ventricular developed pressure (LVDP : -40%) together with a stimulation of glycolytic flux secondary to PK activation. In contrast, adenosine primarily reduced heart rate (HR: -30%) with only marginal effects on LVDP. This was associated with an inhibition of glycolysis at the level of PK. The Na+ ionophore monensin affected HR (+14%) and LVDP (+25%). This effect was associated with a stimulation of glycolysis secondary to the stimulation of PK. These results provide new information of action of adenosine in the heart and support the concept of a direct coupling between glycolysis and process regulating sarcolemmal ionic fluxes.

Effects of KATP channel modulation on myocardial glycogen content, lactate, and amino acids in nonischemic and ischemic rat hearts

ATP-sensitive potassium (KATP) channels are involved in the mechanisms underlying ischemic preconditioning. KATP channels open during ischemia, presumably secondary to intracellular metabolic alterations. The direct effects of KATP channel modulation on myocardial metabolism have not been studied. The aim of the present study was to investigate whether a KATP opener (diazoxide) and blocker (glibenclamide) modulates myocardial glycogen, lactate, and amino acid content before, during, and after ischemia. In isolated perfused rat hearts, we investigated the effect of diazoxide (30 microM) and glibenclamide (10 microM) administered 15 minutes before ischemia on myocardial glycogen, lactate, and amino acid content before, during, and after ischemia. Diazoxide increased left-ventricular developed pressure during reperfusion (P < 0.05) and decreased myocardial glycogen depletion (P < 0.05) and lactate accumulation (P < 0.05) during ischemia compared with the control group. Glibenclamide decreased myocardial glycogen content (P < 0.05) and increased myocardial lactate (P < 0.05) and alanine (P < 0.05) content before ischemia and reduced myocardial glycogen content after ischemia (P < 0.05) compared with control. KATP channel activation by diazoxide modulates myocardial metabolism. These findings suggest that activation of KATP channels protects against ischemia-reperfusion injury by a mechanism that involves decreased energy depletion.