Pyruvate potentiates inotropic effects of isoproterenol and Ca(2+) in rabbit cardiac muscle preparations

Investigating the inotropic effect of pyruvic acid on the isolated rat heart and its underlying mechanism

Pyruvic acid is important organic chemical intermediates that plays a role in cardiomyocyte pathophysiology and therapy. This study sought to explore the inotropic effects of pyruvic acid on the function of the isolated rat hearts and investigate its underlying mechanism. Pyruvic acid produced a greater negative inotropic effect compared to HCl and sodium pyruvate in a concentration-dependent pattern in the hearts. The role of low dose of pyruvic acid on heart function was regulated by pyruvic acid molecules and high dose pyruvic acid may be influenced by pyruvic acid molecules and pH. K_v channels may be involved in the pyruvic acid-induced negative inotropic effect. Finally, pyruvic acid markedly increased the level of LDH and CK and reduced the level of Ca²⁺Mg²⁺-ATPase and Na⁺K⁺-ATPase. These results suggest that pyruvic acid may modulate cardiac function at physiological or low doses but can cause damage to cardiomyocytes at high doses.

Matrix revisited: mechanisms linking energy substrate metabolism to the function of the heart

Metabolic signaling mechanisms are increasingly recognized to mediate the cellular response to alterations in workload demand, as a consequence of physiological and pathophysiological challenges. Thus, an understanding of the metabolic mechanisms coordinating activity in the cytosol with the energy-providing pathways in the mitochondrial matrix becomes critical for deepening our insights into the pathogenic changes that occur in the stressed cardiomyocyte. Processes that exchange both metabolic intermediates and cations between the cytosol and mitochondria enable transduction of dynamic changes in contractile state to the mitochondrial compartment of the cell. Disruption of such metabolic transduction pathways has severe consequences for the energetic support of contractile function in the heart and is implicated in the pathogenesis of heart failure. Deficiencies in metabolic reserve and impaired metabolic transduction in the cardiomyocyte can result from inherent deficiencies in metabolic phenotype or maladaptive changes in metabolic enzyme expression and regulation in the response to pathogenic stress. This review examines both current and emerging concepts of the functional linkage between the cytosol and the mitochondrial matrix with a specific focus on metabolic reserve and energetic efficiency. These principles of exchange and transport mechanisms across the mitochondrial membrane are reviewed for the failing heart from the perspectives of chronic pressure overload and diabetes mellitus.

The positive inotropic effect of pyruvate involves an increase in myofilament calcium sensitivity

Pyruvate is a metabolic fuel that is a potent inotropic agent. Despite its unique inotropic and antioxidant properties, the molecular mechanism of its inotropic mechanism is still largely unknown. To examine the inotropic effect of pyruvate in parallel with intracellular calcium handling under near physiological conditions, we measured pH, myofilament calcium sensitivity, developed force, and calcium transients in ultra thin rabbit heart trabeculae at 37 °C loaded iontophoretically with the calcium indicator bis-fura-2. By contrasting conditions of control versus sarcoplasmic reticulum block (with either cyclopiazonic acid and ryanodine or with thapsigargin) we were able to characterize and isolate the effects of pyruvate on sarcoplasmic reticulum calcium handling and developed force. A potassium contracture technique was subsequently utilized to assess the force-calcium relationship and thus the myofilament calcium sensitivity. Pyruvate consistently increased developed force whether or not the sarcoplasmic reticulum was blocked (16.8±3.5 to 24.5±5.1 vs. 6.9±2.6 to 12.5±4.4 mN/mm(2), non-blocked vs. blocked sarcoplasmic reticulum respectively, p<0.001, n = 9). Furthermore, the sensitizing effect of pyruvate on the myofilaments was demonstrated by potassium contractures (EC50 at baseline versus 20 minutes of pyruvate infusion (peak force development) was 701±94 vs. 445±65 nM, p<0.01, n = 6). This study is the first to demonstrate that a leftward shift in myofilament calcium sensitivity is an important mediator of the inotropic effect of pyruvate. This finding can have important implications for future development of therapeutic strategies in the management of heart failure.

Intracoronary pyruvate in cardiogenic shock as an adjunctive therapy to catecholamines and intra-aortic balloon pump shows beneficial effects on hemodynamics

Aims

Pyruvate was shown to increase cardiac performance in isolated human and animal myocardium and in patients with chronic heart failure. We sought to investigate the effects of pyruvate in acute heart failure.

Methods and results

Patients presenting with cardiogenic shock because of acute myocardial infarction were subjected to standard care with primary PCI and intra-aortic balloon pump (IABP). Then, a Swan–Ganz catheter was placed in the pulmonary artery and hemodynamics was analyzed before, during and after intracoronary administration of 300 mmol/L pyruvate (360 ml/h). Pyruvate induced a significant increase in cardiac index (CI 2.23 ± 0.53 vs. 1.95 ± 0.45 L min⁻¹ m⁻²; p < 0.05), stroke volume index (SVI, 29 ± 6 vs. 26 ± 5 mL m⁻²; p < 0.05), and mean systemic arterial pressure (mean SAP, 95 ± 9 vs. 87 ± 9 mmHg; p < 0.05), whereas heart rate did not significantly change. The effects occurred rapidly within 30 min and were reversible within 10 min.

Conclusion

Intracoronary pyruvate might show beneficial effects in severe acute heart failure in addition to treatment with catecholamines and IABP. These effects should be further investigated in randomized controlled trials.

Elevated afterload, neuroendocrine stimulation, and human heart failure increase BNP levels and inhibit preload-dependent SERCA upregulation

BACKGROUND

In heart failure, brain-type natriuretic peptide (BNP) is elevated and the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) downregulated. We previously showed that preload-induced SERCA-upregulation is suppressed by exogenous BNP.

METHODS AND RESULTS

Here we tested the hypothesis that afterload and neurohumoral activation would counterregulate preload-dependent SERCA upregulation through BNP, which finally results in decreased SERCA levels. We studied the effects of 6 hours preload, afterload, and isoproterenol stimulation on BNP and SERCA mRNA expression in rabbit and human failing muscles strips. Preload resulted in a pronounced upregulation of SERCA by 149% (isotonic versus slack, P<0.01). This upregulation was largely suppressed in afterloaded muscles (isometric versus slack: +32%; P<0.05). Similarly, presence of isoproterenol prevented SERCA upregulation in isotonic muscles. Afterload and isoproterenol resulted in a pronounced increase in BNP expression compared with slack by 225% (P<0.05) and 198% (P<0.01), respectively. Isoproterenol also increased expression of phospholamban by 84% (P<0.01). SERCA upregulation in preloaded muscles is associated with frequency-dependent potentiation of contractile force, which is absent in afterloaded muscles. In failing human myocardium, BNP expression was upregulated compared with nonfailing (+631%; P<0.05). Neither unloading nor preload or afterload induced a change in SERCA or BNP expression after 6 hours.

CONCLUSIONS

Afterload and neuroendocrine stimulation increase BNP expression thereby causing inhibition of preload-dependent SERCA upregulation. In failing human myocardium, high BNP expression may underlie the loss of preload-dependent upregulation of SERCA. BNP may thus contribute to adverse myocardial remodelling in heart failure.

In vivo assessment of pyruvate dehydrogenase flux in the heart using hyperpolarized carbon-13 magnetic resonance

The advent of hyperpolarized (13)C magnetic resonance (MR) has provided new potential for the real-time visualization of in vivo metabolic processes. The aim of this work was to use hyperpolarized [1-(13)C]pyruvate as a metabolic tracer to assess noninvasively the flux through the mitochondrial enzyme complex pyruvate dehydrogenase (PDH) in the rat heart, by measuring the production of bicarbonate (H(13)CO(3)(-)), a byproduct of the PDH-catalyzed conversion of [1-(13)C]pyruvate to acetyl-CoA. By noninvasively observing a 74% decrease in H(13)CO(3)(-) production in fasted rats compared with fed controls, we have demonstrated that hyperpolarized (13)C MR is sensitive to physiological perturbations in PDH flux. Further, we evaluated the ability of the hyperpolarized (13)C MR technique to monitor disease progression by examining PDH flux before and 5 days after streptozotocin induction of type 1 diabetes. We detected decreased H(13)CO(3)(-) production with the onset of diabetes that correlated with disease severity. These observations were supported by in vitro investigations of PDH activity as reported in the literature and provided evidence that flux through the PDH enzyme complex can be monitored noninvasively, in vivo, by using hyperpolarized (13)C MR.

Influence of pyruvate on economy of contraction in isolated rabbit myocardium

BACKGROUND

Treatment of acute heart failure frequently requires positive-inotropic stimulation. However, there is still no inotropic agent available, which combines a favourable haemodynamic profile with low expenditure for energy metabolism. Pyruvate exhibits positive inotropic effects in vitro and in patients with heart failure. The effect on myocardial energy metabolism however remains unclear, but is meaningful in light of a clinical application.

AIMS AND METHODS

We investigated the influence of pyruvate on contractility and oxygen consumption in isolated isometric contracting rabbit myocardium compared to beta-adrenergic stimulation with isoproterenol.

RESULTS

Pyruvate (30 mM) increased developed force from 18.7+/-4.1 to 50.8+/-12.1 mN/mm2 (n=10, p<0.01). Force-time integral (FTI) increased by 329%, oxygen consumption assessed by diffusion-microelectrode technique increased from 2.86+/-0.30 mlO2/min*100 g to 6.28+/-1.28 mlO2/min*100 g (n=7, p<0.05). Economy of myocardial contraction calculated as the ratio of total FTI to oxygen consumption remained unchanged. In contrast, while isoproterenol (10 microM) produced a comparable increase in developed force from 21.4+/-8.3 to 67.3+/-15 mN/mm2 (n=7, p<0.01), FTI increased only by 260% and MVO2 increased from 2.96+/-0.43 to 6.12+/-1.01 mlO2/min*100 g (n=7, p<0.01); thus, economy decreased by 23% (n=7, p<0.05).

CONCLUSION

Pyruvate does not impair economy of myocardial contraction while isoproterenol decreases economy. Regarding energy expenditure, pyruvate appears superior to isoproterenol for the purpose of positive inotropic stimulation.

Direct in vivo monitoring of sarcoplasmic reticulum Ca2+ and cytosolic cAMP dynamics in mouse skeletal muscle

Skeletal muscle contraction depends on the release of Ca(2+) from the sarcoplasmic reticulum (SR), but the dynamics of the SR free Ca(2+) concentration ([Ca(2+)](SR)), its modulation by physiological stimuli such as catecholamines, and the concomitant changes in cAMP handling have never been directly determined. We used two-photon microscopy imaging of GFP-based probes expressed in mouse skeletal muscles to monitor, for the first time in a live animal, the dynamics of [Ca(2+)](SR) and cAMP. Our data, which were obtained in highly physiological conditions, suggest that free [Ca(2+)](SR) decreases by approximately 50 microM during single twitches elicited through nerve stimulation. We also demonstrate that cAMP levels rise upon beta-adrenergic stimulation, leading to an increased efficacy of the Ca(2+) release/reuptake cycle during motor nerve stimulation.

Pyruvate improves cardiac electromechanical and metabolic recovery from cardiopulmonary arrest and resuscitation

Severe depletion of myocardial energy and antioxidant resources during cardiac arrest culminates in electromechanical dysfunction following recovery of spontaneous circulation (ROSC). A metabolic fuel and natural antioxidant, pyruvate augments myocardial energy and antioxidant redox states in parallel with its enhancement of contractile performance of stunned and oxidant-challenged hearts. This study tested whether pyruvate improves post-arrest cardiac function and metabolism. Beagles were subjected to 5 min cardiac arrest and 5 min open-chest cardiac compression (OCCC: 80 compressions min(-1); aortic pressure 60-70 mmHg), then epicardial dc countershocks (5-10 J) were applied to restore sinus rhythm. Pyruvate was infused i.v. throughout OCCC and the first 25 min ROSC to a steady-state arterial concentration of 3.6+/-0.2 mM. Control experiments received NaCl infusions. Phosphocreatine phosphorylation potential (approximately PCr) and glutathione/glutathione disulfide ratio (GSH/GSSG), measured in snap-frozen left ventricle, indexed energy and antioxidant redox states, respectively. In control experiments, left ventricular pressure development, dP/dt and carotid flow initially recovered upon defibrillation, but then fell 40-50% by 3 h ROSC. ST segment displacement in lead II ECG persisted throughout ROSC. Approximately PCr collapsed and GSH/GSSG fell 61% during arrest. Both variables recovered partially during OCCC and completely during ROSC. Pyruvate temporarily increased approximately PCr and GSH/GSSG during OCCC and the first 25 min ROSC and enhanced pressure development, dP/dt and carotid flow at 15-25 min ROSC. Contractile function stabilized and ECG normalized at 2-3 h ROSC, despite post-infusion pyruvate clearance and waning of its metabolic benefits. In conclusion, intravenous pyruvate therapy increases energy reserves and antioxidant defenses of resuscitated myocardium. These temporary metabolic improvements support post-arrest recovery of cardiac electromechanical performance.

Myocardial substrate metabolism in the normal and failing heart

The alterations in myocardial energy substrate metabolism that occur in heart failure, and the causes and consequences of these abnormalities, are poorly understood. There is evidence to suggest that impaired substrate metabolism contributes to contractile dysfunction and to the progressive left ventricular remodeling that are characteristic of the heart failure state. The general concept that has recently emerged is that myocardial substrate selection is relatively normal during the early stages of heart failure; however, in the advanced stages there is a downregulation in fatty acid oxidation, increased glycolysis and glucose oxidation, reduced respiratory chain activity, and an impaired reserve for mitochondrial oxidative flux. This review discusses 1) the metabolic changes that occur in chronic heart failure, with emphasis on the mechanisms that regulate the changes in the expression of metabolic genes and the function of metabolic pathways; 2) the consequences of these metabolic changes on cardiac function; 3) the role of changes in myocardial substrate metabolism on ventricular remodeling and disease progression; and 4) the therapeutic potential of acute and long-term manipulation of cardiac substrate metabolism in heart failure.

Metabolic cardioprotection by pyruvate: recent progress

Pyruvate, a natural metabolic fuel and antioxidant in myocardium and other tissues, exerts a variety of cardioprotective actions when provided at supraphysiological concentrations. Pyruvate increases cardiac contractile performance and myocardial energy state, bolsters endogenous antioxidant systems, and protects myocardium from ischemia-reperfusion injury and oxidant stress. This article reviews and discusses basic and clinically oriented research conducted over the last several years that has yielded fundamental information on pyruvate's inotropic and cardioprotective mechanisms. Particular attention is placed on pyruvate's enhancement of sarcoplasmic reticular Ca2+ transport, its antioxidant properties, and its ability to mitigate reversible and irreversible myocardial injury. These research efforts are establishing the essential foundation for clinical application of pyruvate therapy in numerous settings including cardiopulmonary bypass surgery, cardiopulmonary resuscitation, myocardial stunning, and cardiac failure.

Antioxidant properties of myocardial fuels

Oxidative metabolism of blood-borne fuels provides myocardium the energy required to sustain its contractile performance. Recent research has revealed that, in addition to supplying energy, certain fuels are able to detoxify harmful oxidants and bolster the myocardium's endogenous antioxidant defenses. These antioxidant capabilities could potentially protect the myocardium from the ravages of reactive oxygen and nitrogen intermediates generated upon reperfusion of ischemic myocardium. This article reviews experimental evidence that two fuels, pyruvate and acetoacetate, provide such antioxidant protection. Pyruvate's antioxidant properties stem in part from its alpha-keto carboxylate structure, which enables it to directly, non-enzymatically neutralize peroxides and peroxynitrite. Also, citrate, which accumulates in pyruvate-perfused myocardium following anaplerotic pyruvate carboxylation, supports NADPH production to maintain glutathione:glutathione disulfide (GSH/GSSG) redox potential, the central component of the myocardial antioxidant system. Like pyruvate, acetoacetate restores GSH/GSSG and increases contractile function of post-ischemic stunned myocardium, although some of its antioxidant mechanisms may differ from pyruvate's. Both compounds restore beta-adrenergic signaling and inotropism, which are compromised in stunned myocardium. N-acetylcysteine, a pharmacological antioxidant that does not provide energy, duplicated the salutary effects of pyruvate and acetoacetate on post-ischemic gamma-adrenergic signaling and GSH/GSSG. These findings reveal novel, energy-independent mechanisms for enhancement of post-ischemic cardiac performance by metabolic fuels.

Improved systolic and diastolic myocardial function with intracoronary pyruvate in patients with congestive heart failure

BACKGROUND

Pyruvate increases myocardial performance in isolated myocardium and improves hemodynamics in patients with congestive heart failure.

AIMS

To investigate the influence of pyruvate on detailed parameters of systolic and diastolic left ventricular (LV) function.

METHODS AND RESULTS

In patients with heart failure due to dilated cardiomyopathy (LVEF 30+/-4%, n=9) pyruvate was infused intracoronarily. LV function was analysed before, during and after application of different pyruvate concentrations using a LV-micromanometer catheter. LV volumes were determined using cine ventriculography. Pyruvate increased maximum rate of LV isovolumic pressure rise (Peak +dP/dt) from 802+/-106 to 1125+/-103 mmHg/s (P<0.05). Left ventricular end-diastolic pressure declined in parallel from 17+/-2 to 12+/-2 mmHg (P<0.05) and heart rate decreased from 79+/-4 to 72+/-5 min(-1) (P<0.05). Stroke volume index increased from 34+/-4 to 43+/-6 ml/m(2) (P<0.05), end-diastolic LV volume remained unchanged, thus left ventricular ejection fraction increased with pyruvate from 30+/-4 to 39+/-4% (P<0.05). Maximum rate of LV isovolumic pressure decline (Peak -dP/dt) was significantly increased with pyruvate (from 794+/-94 to 980+/-108 mmHg/s; P<0.05) and mean arterial pressure increased from 80+/-5 to 88+/-4 mmHg (P<0.05). Discontinuation of pyruvate resulted in immediate reversibility of its effects.

CONCLUSION

Intracoronary pyruvate improves systolic and diastolic myocardial function and increases ejection fraction without increasing heart rate. Pyruvate thus exhibits the profile of a favourable inotropic agent, however, further investigation for the treatment of patients with acute heart failure is mandatory.

The intermediary metabolite pyruvate attenuates stunning and reduces infarct size in in vivo porcine myocardium

The intermediary metabolite pyruvate has been shown to exert significant beneficial effects in in vitro models of myocardial oxidative stress and ischemia-reperfusion injury. However, there have been few reports of the ability of pyruvate to attenuate myocardial stunning or reduce infarct size in vivo. This study tested whether supraphysiological levels of pyruvate protect against reversible and irreversible in vivo myocardial ischemia-reperfusion injury. Anesthetized, open-chest pigs ( n = 7/group) underwent 15 min of left anterior descending coronary artery (LAD) occlusion and 3 h of reperfusion to induce stunning. Load-insensitive contractility measurements of regional preload recruitable stroke work (PRSW) and PRSW area (PRSWA) were generated. Vehicle or pyruvate (100 mg/kg iv bolus + 10 mg·kg–1·min–1 intra-atrial infusion) was administered during ischemia and for the first hour of reperfusion. In infarct studies, pigs ( n = 6/group) underwent 1 h of LAD ischemia and 3 h of reperfusion. Group I pigs received vehicle or pyruvate for 30 min before and throughout ischemia. In group II, the infusion was extended through 1 h of reperfusion. In the stunning protocol, pyruvate significantly improved the recovery of PRSWA at 1 h (50 ± 4% vs. 23 ± 3% in controls) and 3 h (69 ± 5% vs. 39 ± 3% in controls) reperfusion. Control pigs exhibited infarct sizes of 66 ± 1% of the area at risk. The pyruvate I protocol was associated with an infarct size of 49 ± 3% ( P < 0.05), whereas the pyruvate II protocol was associated with an infarct size of 30 ± 2% ( P < 0.05 vs. control and pyruvate I). These findings suggest that pyruvate attenuates stunning and decreases myocardial infarction in vivo in part by reduction of reperfusion injury. Metabolic interventions such as pyruvate should be considered when designing the optimal therapeutic strategies for limiting myocardial ischemia-reperfusion injury.

Dose-dependent effects of ethyl pyruvate in mice subjected to mesenteric ischemia and reperfusion

OBJECTIVE

We previously showed that infusing rats with a solution of ethyl pyruvate ameliorates intestinal mucosal injury after mesenteric ischemia and reperfusion. Ethyl pyruvate also has been shown to inhibit the expression of various pro-inflammatory cytokines in several animal models of critical illness, but dose-response relationships have not been investigated.

DESIGN

Anesthetized C57BL/6 mice were subjected to 60 min of mesenteric ischemia followed by 60 min of reperfusion. After 55 min of ischemia, groups of mice were treated with normal saline or graded bolus doses of ethyl pyruvate dissolved in a calcium-containing balanced salt solution. Some animals (i.e., those in the sham group) were subjected to the anesthetic, but not mesenteric ischemia/reperfusion. Gut mucosal permeability was assessed using an everted gut sac technique.

SETTING

University research laboratory.

MEASUREMENTS AND RESULTS

Mesenteric ischemia/reperfusion significantly increased ileal mucosal permeability to the hydrophilic macromolecule, fluorescein isothiocyanate dextran (molecular mass 4,000 Da). Whereas the lowest dose of ethyl pyruvate evaluated (17 mg/kg) had no effect on gut mucosal permeability, the two highest doses tested (50 and 150 mg/kg) significantly ameliorated the development of ischemia/reperfusion-induced mucosal hyperpermeability to about the same extent. The two highest doses of ethyl pyruvate also significantly ameliorated deficits in ileal serosal and mucosal and hepatic surface microvascular perfusion induced by mesenteric ischemia/reperfusion. Ethyl pyruvate inhibited post-ischemia/reperfusion hepatic NF-kappaB activation and TNF mRNA expression in a dose-dependent fashion.

CONCLUSION

Doses of ethyl pyruvate equal to or greater than 50 mg/kg ameliorate inflammation, microvascular hypoperfusion and gut mucosal damage induced by mesenteric ischemia/reperfusion in mice.

Pyruvate modulates cardiac sarcoplasmic reticulum Ca2+ release in rats via mitochondria-dependent and -independent mechanisms

The glycolytic product pyruvate has beneficial effects on cardiac contractile function. The postulated cellular mechanisms underlying the positive inotropic effect of pyruvate, however, are contradictory or have remained elusive. Therefore, we studied the effects of pyruvate on cardiac Ca2+ regulation, intracellular pH (pHi) and flavoprotein oxidation using fluorescence confocal microscopy in intact and permeabilized rat ventricular myocytes and single channel recordings from rat cardiac ryanodine receptors (RyRs) incorporated into planar lipid bilayers. In intact cells extracellular pyruvate (10 mM) elevated diastolic [Ca2+]i, which was due, at least in part, to a concomitant acidification of the cytosol. Furthermore, pyruvate increased the amplitude and slowed the kinetics of the electrically evoked [Ca2+]i transient, and augmented sarcoplasmic reticulum (SR) Ca2+ content. Recording of flavoprotein (FAD) fluorescence indicated that pyruvate caused a reduction of mitochondrial redox potential, which is proportional to an increase of the rate of ATP synthesis. Inhibitors of mitochondrial monocarboxylate transport (alpha-cyano-4-hydroxycinnamate, 0.5 mM), adenine nucleotide translocation (atractyloside, 0.3 mM) and the electron transport chain (cyanide, 4 mM) abolished or attenuated the pyruvate-mediated increase of the amplitude of the [Ca2+]i transient, but did not change the effect of pyruvate on diastolic [Ca2+]i. Results from experiments with permeabilized myocytes indicated a direct correlation between ATP/ADP ratio and SR Ca2+ content. Furthermore, pyruvate (4 mM) reduced the frequency of spontaneous Ca2+ sparks by approximately 50%. Single RyR channel recordings revealed a approximately 60% reduction of the open probability of the channel by pyruvate (1 mM), but no change in conductance. This effect of pyruvate on RyR channel activity was neither Ca2+ nor ATP dependent. Taken together, these findings suggest that, in cardiac tissue, pyruvate has a dual effect on SR Ca2+ release consisting of a direct inhibition of RyR channel activity and elevation of SR Ca2+ content. The latter effect was most probably mediated by an enhanced SR Ca2+ uptake due to an augmentation of mitochondria-dependent ATP synthesis.

Upregulation of the cardiac monocarboxylate transporter MCT1 in a rat model of congestive heart failure

BACKGROUND

Cardiac metabolism becomes more dependent on carbohydrates in congestive heart failure (CHF), and lactate may be used as an important respiratory substrate. Monocarboxylate transporter 1 (MCT1) promotes cotransport of lactate and protons into and out of heart cells and conceivably flux of lactate between cells, because it is abundantly present in the intercalated disk.

METHODS AND RESULTS

Six weeks after induction of myocardial infarction (MI) in Wistar rats, left ventricular end-diastolic pressures were >15 mm Hg, signifying CHF. MCT1 and connexin43 protein levels in CHF were 260% and 20%, respectively, of those in sham-operated animals (Sham), and the corresponding mRNA signals were 181% and not significantly changed, respectively. Confocal laserscan immunohistochemistry and quantitative immunogold cytochemistry showed that MCT1 density was much higher in CHF than in Sham both at the surface membrane and in the intercalated disk. In CHF, a novel intracellular pool of MCT1 appeared to be associated with cisternae, some close to the T tubules. In contrast, connexin43 particles, seen exclusively at gap junctions, were substantially fewer. Maximum lactate uptake was 107+/-15 mmol. L(-1). min(-1) in CHF and 42+/-6 mmol. L(-1). min(-1) in Sham cells (P<0.05). The K(m) values were between 7 and 9 mmol/L (P=NS).

CONCLUSIONS

In cardiomyocytes from CHF rats, (1) the amount of functional MCT1 in the sarcolemma, including in the intercalated disk, is increased several-fold; (2) a new intracellular pool of MCT1 appears; (3) another disk protein, connexin43, is much reduced; and (4) increased reliance on lactate and other monocarboxylates (eg, pyruvate) could provide tight metabolic control of high-energy phosphates.