Retraction notice to "Cardiac-specific overexpression of catalase attenuates lipopolysaccharide-induced myocardial contractile dysfunction: Role of autophagy" [Free Radic. Biol. Med. 53/6 (2012) 1327-1338].

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. After an institutional investigation into the work of Dr. Jun Ren, University of Wyoming subsequently conducted an examination of other selected publications of Dr. Ren's under the direction of the HHS Office of Research Integrity. Based on the findings of this examination, the University of Wyoming recommended this article be retracted due to concerns regarding data irregularities inconsistent with published conclusions. Specifically, University of Wyoming found evidence of data irregularities and image reuse in Figure 2 that significantly affect the results and conclusions reported in the manuscript.

Increasing Fatty Acid Oxidation Prevents High-Fat Diet-Induced Cardiomyopathy Through Regulating Parkin-Mediated Mitophagy.

BACKGROUND: Increased fatty acid oxidation (FAO) has long been considered a culprit in the development of obesity/diabetes mellitus-induced cardiomyopathy. However, enhancing cardiac FAO by removing the inhibitory mechanism of long-chain fatty acid transport into mitochondria via deletion of acetyl coenzyme A carboxylase 2 (ACC2) does not cause cardiomyopathy in nonobese mice, suggesting that high FAO is distinct from cardiac lipotoxicity. We hypothesize that cardiac pathology-associated obesity is attributable to the imbalance of fatty acid supply and oxidation. Thus, we here seek to determine whether further increasing FAO by inducing ACC2 deletion prevents obesity-induced cardiomyopathy, and if so, to elucidate the underlying mechanisms. METHODS: We induced high FAO in adult mouse hearts by cardiac-specific deletion of ACC2 using a tamoxifen-inducible model (ACC2 iKO). Control and ACC2 iKO mice were subjected to high-fat diet (HFD) feeding for 24 weeks to induce obesity. Cardiac function, mitochondria function, and mitophagy activity were examined. RESULTS: Despite both control and ACC2 iKO mice exhibiting a similar obese phenotype, increasing FAO oxidation by deletion of ACC2 prevented HFD-induced cardiac dysfunction, pathological remodeling, and mitochondria dysfunction, as well. Similarly, increasing FAO by knockdown of ACC2 prevented palmitate-induced mitochondria dysfunction and cardiomyocyte death in vitro. Furthermore, HFD suppressed mitophagy activity and caused damaged mitochondria to accumulate in the heart, which was attenuated, in part, in the ACC2 iKO heart. Mechanistically, ACC2 iKO prevented HFD-induced downregulation of parkin. During stimulation for mitophagy, mitochondria-localized parkin was severely reduced in control HFD-fed mouse heart, which was restored, in part, in ACC2 iKO HFD-fed mice. CONCLUSIONS: These data show that increasing cardiac FAO alone does not cause cardiac dysfunction, but protects against cardiomyopathy in chronically obese mice. The beneficial effect of enhancing cardiac FAO in HFD-induced obesity is mediated, in part, by the maintenance of mitochondria function through regulating parkin-mediated mitophagy. Our findings also suggest that targeting the parkin-dependent mitophagy pathway could be an effective strategy against the development of obesity-induced cardiomyopathy.

The Role of Diacylglycerol Acyltransferase (DGAT) 1 and 2 in Cardiac Metabolism and Function.

It is increasingly recognized that synthesis and turnover of cardiac triglyceride (TG) play a pivotal role in the regulation of lipid metabolism and function of the heart. The last step in TG synthesis is catalyzed by diacylglycerol:acyltransferase (DGAT) which esterifies the diacylglycerol with a fatty acid. Mammalian heart has two DGAT isoforms, DGAT1 and DGAT2, yet their roles in cardiac metabolism and function remain poorly defined. Here, we show that inactivation of DGAT1 or DGAT2 in adult mouse heart results in a moderate suppression of TG synthesis and turnover. Partial inhibition of DGAT activity increases cardiac fatty acid oxidation without affecting PPARα signaling, myocardial energetics or contractile function. Moreover, coinhibition of DGAT1/2 in the heart abrogates TG turnover and protects the heart against high fat diet-induced lipid accumulation with no adverse effects on basal or dobutamine-stimulated cardiac function. Thus, the two DGAT isoforms in the heart have partially redundant function, and pharmacological inhibition of one DGAT isoform is well tolerated in adult hearts.

The effects of fatty acid composition on cardiac hypertrophy and function in mouse models of diet-induced obesity.

High-fat diets (HFDs) are used frequently to study the development of cardiac dysfunction in animal models of obesity and diabetes. However, impairment in systolic function, often reported as declining ejection fraction, may not consistently occur in a given time frame which could be contributable to a variety of factors within the experimental design. One major factor may be the amounts of saturated and unsaturated fatty acids (FAs) that are present in the diet. To determine whether the FA content and composition were critical determinants in the development of cardiac dysfunction in response to high-fat feeding, we fed adult, male mice Western diet (45% fat, 60% saturated), Surwit diet (60% fat, 90% saturated), milk-fat-based diet (60% fat, 60% saturated) or high-fat Western diet (HFWD, 60% fat, 32% saturated) for 12 weeks. We report that neither the amount of total fat nor the ratio of saturated to unsaturated FAs in the diets differentially affects body weight and adiposity in mice. In addition, no evidence of systolic dysfunction is present after 12 weeks. Interestingly, the HFWD, with equal parts saturated, monounsaturated and polyunsaturated FAs, induces mild cardiac hypertrophy and diastolic dysfunction after 12 weeks, which coincides with elevated serum levels of arachidonic acid. Our results suggest that the dietary FA content and composition may be a primary determinant of diastolic, but not systolic, dysfunction in animal models of diet-induced obesity.

Defective Branched-Chain Amino Acid Catabolism Disrupts Glucose Metabolism and Sensitizes the Heart to Ischemia-Reperfusion Injury.

Elevated levels of branched-chain amino acids (BCAAs) have recently been implicated in the development of cardiovascular and metabolic diseases, but the molecular mechanisms are unknown. In a mouse model of impaired BCAA catabolism (knockout [KO]), we found that chronic accumulation of BCAAs suppressed glucose metabolism and sensitized the heart to ischemic injury. High levels of BCAAs selectively disrupted mitochondrial pyruvate utilization through inhibition of pyruvate dehydrogenase complex (PDH) activity. Furthermore, downregulation of the hexosamine biosynthetic pathway in KO hearts decreased protein O-linked N-acetylglucosamine (O-GlcNAc) modification and inactivated PDH, resulting in significant decreases in glucose oxidation. Although the metabolic remodeling in KO did not affect baseline cardiac energetics or function, it rendered the heart vulnerable to ischemia-reperfusion injury. Promoting BCAA catabolism or normalizing glucose utilization by overexpressing GLUT1 in the KO heart rescued the metabolic and functional outcome. These observations revealed a novel role of BCAA catabolism in regulating cardiac metabolism and stress response.

Normalization of NAD+ Redox Balance as a Therapy for Heart Failure.

BACKGROUND: Impairments of mitochondrial function in the heart are linked intricately to the development of heart failure, but there is no therapy for mitochondrial dysfunction. METHODS: We assessed the reduced/oxidized ratio of nicotinamide adenine dinucleotide (NADH/NAD(+) ratio) and protein acetylation in the failing heart. Proteome and acetylome analyses were followed by docking calculation, mutagenesis, and mitochondrial calcium uptake assays to determine the functional role of specific acetylation sites. The therapeutic effects of normalizing mitochondrial protein acetylation by expanding the NAD(+) pool also were tested. RESULTS: Increased NADH/NAD(+) and protein hyperacetylation, previously observed in genetic models of defective mitochondrial function, also are present in human failing hearts as well as in mouse hearts with pathologic hypertrophy. Elevation of NAD(+) levels by stimulating the NAD(+) salvage pathway suppressed mitochondrial protein hyperacetylation and cardiac hypertrophy, and improved cardiac function in responses to stresses. Acetylome analysis identified a subpopulation of mitochondrial proteins that was sensitive to changes in the NADH/NAD(+) ratio. Hyperacetylation of mitochondrial malate-aspartate shuttle proteins impaired the transport and oxidation of cytosolic NADH in the mitochondria, resulting in altered cytosolic redox state and energy deficiency. Furthermore, acetylation of oligomycin-sensitive conferring protein at lysine-70 in adenosine triphosphate synthase complex promoted its interaction with cyclophilin D, and sensitized the opening of mitochondrial permeability transition pore. Both could be alleviated by normalizing the NAD(+) redox balance either genetically or pharmacologically. CONCLUSIONS: We show that mitochondrial protein hyperacetylation due to NAD(+) redox imbalance contributes to the pathologic remodeling of the heart via 2 distinct mechanisms. Our preclinical data demonstrate a clear benefit of normalizing NADH/NAD(+) imbalance in the failing hearts. These findings have a high translational potential as the pharmacologic strategy of increasing NAD(+) precursors are feasible in humans.

Deletion of protein tyrosine phosphatase 1B rescues against myocardial anomalies in high fat diet-induced obesity: Role of AMPK-dependent autophagy.

Obesity-induced cardiomyopathy may be mediated by alterations in multiple signaling cascades involved in glucose and lipid metabolism. Protein tyrosine phosphatase-1B (PTP1B) is an important negative regulator of insulin signaling. This study was designed to evaluate the role of PTP1B in high fat diet-induced cardiac contractile anomalies. Wild-type and PTP1B knockout mice were fed normal (10%) or high (45%) fat diet for 5months prior to evaluation of cardiac function. Myocardial function was assessed using echocardiography and an Ion-Optix MyoCam system. Western blot analysis was employed to evaluate levels of AMPK, mTOR, raptor, Beclin-1, p62 and LC3-II. RT-PCR technique was employed to assess genes involved in hypertrophy and lipid metabolism. Our data revealed increased LV thickness and LV chamber size as well as decreased fractional shortening following high fat diet intake, the effect was nullified by PTP1B knockout. High fat diet intake compromised cardiomyocyte contractile function as evidenced by decreased peak shortening, maximal velocity of shortening/relengthening, intracellular Ca²âº release as well as prolonged duration of relengthening and intracellular Ca²âº decay, the effects of which were alleviated by PTP1B knockout. High fat diet resulted in enlarged cardiomyocyte area and increased lipid accumulation, which were attenuated by PTP1B knockout. High fat diet intake dampened myocardial autophagy as evidenced by decreased LC3-II conversion and Beclin-1, increased p62 levels as well as decreased phosphorylation of AMPK and raptor, the effects of which were significantly alleviated by PTP1B knockout. Pharmacological inhibition of AMPK using compound C disengaged PTP1B knockout-conferred protection against fatty acid-induced cardiomyocyte contractile anomalies. Taken together, our results suggest that PTP1B knockout offers cardioprotection against high fat diet intake through activation of AMPK. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Targeted deletion of PTEN in cardiomyocytes renders cardiac contractile dysfunction through interruption of Pink1-AMPK signaling and autophagy.

Phosphatase and tensin homolog (PTEN) deleted from chromosome 10 has been implicated in the maintenance of cardiac homeostasis although the underlying mechanism(s) remains elusive. We generated a murine model of cardiomyocyte-specific knockout of PTEN to evaluate cardiac geometry and contractile function, as well as the effect of metformin on PTEN deficiency-induced cardiac anomalies, if any. Cardiac histology, autophagy and related signaling molecules were evaluated. Cardiomyocyte-specific PTEN deletion elicited cardiac hypertrophy and contractile anomalies (echocardiographic and cardiomyocyte contractile dysfunction) associated with compromised intracellular Ca(2+) handling. PTEN deletion-induced cardiac hypertrophy and contractile anomalies were associated with dampened phosphorylation of PTEN-inducible kinase 1 (Pink1) and AMPK. Interestingly, administration of AMPK activator metformin (200mg/kg/d, in drinking H2O for 4weeks) rescued against PTEN deletion-induced geometric and functional defects as well as interrupted autophagy and autophagic flux in the heart. Moreover, metformin administration partially although significantly attenuated PTEN deletion-induced accumulation of superoxide. RNA interference against Pink1 in H9C2 myoblasts overtly increased intracellular ATP levels and suppressed AMPK phosphorylation, confirming the role of AMPK as a downstream target for PTEN-Pink1. Further scrutiny revealed that activation of AMPK and autophagy using metformin and rapamycin, respectively, rescued against PTEN deletion-induced mechanical anomalies with little additive effect. These data demonstrated that cardiomyocyte-specific deletion of PTEN leads to the loss of Pink1-AMPK signaling, development of cardiac hypertrophy and contractile defect. Activation of AMPK rescued against PTEN deletion-induced cardiac anomalies associated with restoration of autophagy and autophagic flux. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Inhibition of mammalian target of rapamycin with rapamycin reverses hypertrophic cardiomyopathy in mice with cardiomyocyte-specific knockout of PTEN.

The role of phosphatase and tensin homolog deleted from chromosome 10 (PTEN) in the maintenance of cardiac homeostasis still remains controversial. This study was designed to evaluate the role of cardiomyocyte-specific PTEN in the maintenance of cardiac homeostasis and the underlying mechanisms involved with a focus on autophagy, an evolutionarily conserved pathway for protein degradation. Cardiomyocyte-specific PTEN((flox/flox))/α-myosin heavy chain Cre mice, henceforth referred to as CM-PTENKO, were generated by crossing the floxed PTEN mice with α-myosin heavy chain Cre mice driven by a Cre recombinase promoter. The adult PTEN(-/-) mice displayed the phenotype of established hypertrophic cardiomyopathy, including unfavorable geometric, functional, and histological changes. Furthermore, cardiomyocyte-specific PTEN knockout mice exhibited increased cardiac mammalian target of rapamycin although suppressed autophagy. Treatment with rapamycin (2 mg/kg per day, IP), an inhibitor of mammalian target of rapamycin, for 1 month effectively reversed the established hypertrophic cardiomyopathy in CM-PTENKO mice. With rapamycin treatment, autophagy activity was significantly restored in the heart of CM-PTENKO mice. Taken together, our results demonstrate an essential role for cardiomyocyte PTEN in maintaining cardiac homeostasis under physiological condition. Cardiomyocyte-specific deletion of PTEN results in the development of hypertrophic cardiomyopathy possibly through a mechanism associated with mammalian target of rapamycin hyperactivation and autophagy suppression.

Autophagy inhibition rescues against leptin-induced cardiac contractile dysfunction.

Leptin hormone plays a vital role in the pathophysiological changes in heart geometry and function. Nonetheless, the precise mechanism(s) triggering leptin-induced cardiomyocyte contractile dysfunction is not well understood. The present study was designed to examine if autophagy plays a role in leptin-induced cardiac contractile anomalies. Cardiomyocyte contractile function was evaluated using an IonOptix edge detection system in cardiomyocytes following treatment with leptin in the presence or absence of the autophagy inhibiting chemical 3-methyladenine (3-MA). Immunoblotting was employed to evaluate expression of AMPK, Beclin1, Atg 5, p62 and LC3-II. GFP-LC3 puncta was used to assess autophagosome formation. Leptin suppressed cardiac contractile function as evidenced by decreased peak shortening, maximal velocity of shortening and relengthening, increased time-to-90% relengthening, all the observed effects were reduced or obliterated by autophagy inhibition. Leptin promoted superoxide generation, AMPK activation and overt autophagy induction. Leptin promoted autophagy as evidenced by enhanced LC3-II, Beclin, Atg 5 and decreased p62 levels. Pharmacological inhibition of reactive oxygen species (ROS) using tempol significantly attenuated leptin-induced autophagosome formation and cardiac contractile anomalies. In addition, genetic deletion of AMPKα2 or pharmacological inhibition of AMPK using compound C abrogated leptin or superoxide induced cardiac contractile dysfunction and autophagosome formation. In summary, our data revealed that leptin impairs cardiac contractile function through a superoxide generation-AMPK activation-and autophagy dependent mechanism.

Folic acid reverses nitric oxide synthase uncoupling and prevents cardiac dysfunction in insulin resistance: role of Ca2+/calmodulin-activated protein kinase II.

Nitric oxide synthase (NOS) may be uncoupled to produce superoxide rather than nitric oxide (NO) under pathological conditions such as diabetes mellitus and insulin resistance, leading to cardiac contractile anomalies. Nonetheless, the role of NOS uncoupling in insulin resistance-induced cardiac dysfunction remains elusive. Given that folic acid may produce beneficial effects for cardiac insufficiency partially through its NOS recoupling capacity, this study was designed to evaluate the effect of folic acid on insulin resistance-induced cardiac contractile dysfunction in a sucrose-induced insulin resistance model. Mice were fed a sucrose or starch diet for 8 weeks before administration of folic acid in drinking water for an additional 4 weeks. Cardiomyocyte contractile and Ca(2+) transient properties were evaluated and myocardial function was assessed using echocardiography. Our results revealed whole body insulin resistance after sucrose feeding associated with diminished NO production, elevated peroxynitrite (ONOO(-)) levels, and impaired echocardiographic and cardiomyocyte function along with a leaky ryanodine receptor (RYR) and intracellular Ca(2+) handling derangement. Western blot analysis showed that insulin resistance significantly promoted Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) phosphorylation, which might be responsible for the leaky RYR and cardiac mechanical dysfunction. NOS recoupling using folic acid reversed insulin resistance-induced changes in NO and ONOO(-), CaMKII phosphorylation, and cardiac mechanical abnormalities. Taken together, these data demonstrated that treatment with folic acid may reverse cardiac contractile and intracellular Ca(2+) anomalies through ablation of CaMKII phosphorylation and RYR Ca(2+) leak.

Oxidative activation of Ca(2+)/calmodulin-activated kinase II mediates ER stress-induced cardiac dysfunction and apoptosis.

Endoplasmic reticulum (ER) stress elicits oxidative stress and intracellular Ca(2+) derangement via activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). This study was designed to examine the role of CaMKII in ER stress-induced cardiac dysfunction and apoptosis as well as the effect of antioxidant catalase. Wild-type FVB and transgenic mice with cardiac-specific overexpression of catalase were challenged with the ER stress inducer tunicamycin (3 mg/kg ip for 48 h). Presence of ER stress was verified using the ER stress protein markers immunoglobulin binding protein (BiP) and C/EBP homologous protein (CHOP), the effect of which was unaffected by catalase overexpression. Echocardiographic assessment revealed that tunicamycin elicited cardiac remodeling (enlarged end-systolic diameter without affecting diastolic and ventricular wall thickness), depressed fractional shortening, ejection fraction, and cardiomyocyte contractile capacity, intracellular Ca(2+) mishandling, accumulation of reactive oxygen species (superoxide production and NADPH oxidase p47phox level), CaMKII oxidation, and apoptosis (evidenced by Bax, Bcl-2/Bax ratio, and TUNEL staining), the effects of which were obliterated by catalase. Interestingly, tunicamycin-induced cardiomyocyte mechanical anomalies and cell death were ablated by the CaMKII inhibitor KN93, in a manner reminiscent of catalase. These data favored a permissive role of oxidative stress and CaMKII activation in ER stress-induced cardiac dysfunction and cell death. Our data further revealed the therapeutic potential of antioxidant or CaMKII inhibition in cardiac pathological conditions associated with ER stress. This research shows for the first time that contractile dysfunction caused by ER stress is a result of the oxidative activation of the CaMKII pathway.

RETRACTED: Cardiac-specific overexpression of catalase attenuates lipopolysaccharide-induced myocardial contractile dysfunction: Role of autophagy

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. After an institutional investigation into the work of Dr. Jun Ren, University of Wyoming subsequently conducted an examination of other selected publications of Dr. Ren's under the direction of the HHS Office of Research Integrity. Based on the findings of this examination, the University of Wyoming recommended this article be retracted due to concerns regarding data irregularities inconsistent with published conclusions. Specifically, University of Wyoming found evidence of data irregularities and image reuse in Figure 2 that significantly affect the results and conclusions reported in the manuscript.

Nitric oxide synthase uncoupling: a therapeutic target in cardiovascular diseases.

Nitric oxide synthase enzyme (NOS) possesses the unique ability to be "uncoupled" to produce superoxide anion (O(2)(-)) instead of nitric oxide (NO). Reduced NO bioavailability as a result of NOS uncoupling has been speculated to play an essential role in cardiovascular pathologies including dilated cardiomyopathy, ischemia reperfusion injury, endothelial dysfunction, atherosclerosis, hypertension and diabetes mellitus. NO serves many important roles in the heart including stimulation of adenylate cyclase (AC) at low levels or guanalyl cyclase (sGC) at higher levels, or by s-nitrosylation of intracellular Ca(2+) regulatory proteins thus altering excitation-contraction coupling. Not surprisingly, NOS uncoupling is an emerging therapeutic target in cardiovascular diseases. Restoring proper NOS activity by increasing intracellular levels of its cofactor tetrahydrobiopterin (BH4) is effective in the management of hypertensive diastolic dysfunction, ischemia-reperfusion injury, myocardial infarction and endothelial dysfunction. New evidence is constantly emerging highlighting the importance of NOS uncoupling in cardiovascular pathologies thus the purpose of this mini-review is to showcase the new advances and promising treatments for NOS uncoupling in CV disease.

Akt2 knockout mitigates chronic iNOS inhibition-induced cardiomyocyte atrophy and contractile dysfunction despite persistent insulin resistance.

Increased levels of inducible nitric oxide synthase (iNOS) during cardiac stress such as ischemia-reperfusion, sepsis and hypertension may display both beneficial and detrimental roles in cardiac contractile performance. However, the precise role of iNOS in the maintenance of cardiac contractile function remains elusive. This study was designed to determine the impact of chronic iNOS inhibition on cardiac contractile function and the underlying mechanism involved with a special focus on the NO downstream signaling molecule Akt. Male C57 or Akt2 knockout [Akt2(-/-)] mice were injected with the specific iNOS inhibitor 1400W (2 mg/kg/d) or saline for 7 days. Both 1400W and Akt2 knockout dampened glucose and insulin tolerance without additive effects. Treatment of 1400W decreased heart and liver weights as well as cardiomyocyte cross-sectional area in C57 but not Akt2 knockout mice. 1400W but not Akt2 knockout compromised cardiomyocyte mechanical properties including decreased peak shortening and maximal velocity of shortening/relengthening, prolonged relengthening duration, reduced intracellular Ca(2+) release and decay rate, the effects of which were ablated or attenuated by Akt2 knockout. Akt2 knockout but not 1400W increased the levels of intracellular Ca(2+) regulatory proteins including SERCA2a and phospholamban phosphorylation. 1400W reduced the level of anti-apoptotic protein Bcl-2, the effect of which was unaffected by Akt2 knockout. Neither 1400W nor Akt2 knockout significantly affected ER stress, autophagy, the post-insulin receptor signaling Akt, GSK3ß and AMPK, as well as the stress signaling IκB, JNK, ERK and p38 with the exception of elevated IκB phosphorylation with jointed effect of 1400W and Akt2 knockout. Taken together, these data indicated that an essential role of iNOS in the maintenance of cardiac morphology and function possibly through an Akt2-dependent mechanism.

Acute methamphetamine exposure inhibits cardiac contractile function.

Methamphetamine, a commonly seen substance of abuse, has been reported to exert detrimental effect on bodily function including the cardiovascular system although its mechanism of action is poorly understood. This study was designed to examine the direct impact of methamphetamine on isolated whole heart and single cardiomyocyte contractile function. Murine hearts and isolated cardiomyocytes from adult FVB mice were exposed to various concentrations of methamphetamine for 30min prior to the assessment of mechanical function using a Langendroff apparatus and an IonOptix Myocam system, respectively. Cardiac contractile properties analyzed included maximal velocity of left ventricular pressure development and decline (+/-dP/dt), peak shortening amplitude (PS), maximal velocity of shortening/relengthening (+/-dLdt), time-to-PS (TPS), time-to-90% relengthening (TR(90)), resting and electrically stimulated increase of intracellular Ca(2+) as well as intracellular Ca(2+) decay. Our results revealed that acute methamphetamine exposure depressed +/-dP/dt, PS and rise of intracellular Ca(2+) without affecting +/-dLdt, TPS, TR(90), resting intracellular Ca(2+) and intracellular Ca(2+) decay. Furthermore, methamphetamine nullified the adrenergic agonist norepinephrine-elicited positive cardiomyocyte contractile response, including elevated PS, +/-dLdt and shortened TR(90) without affecting TPS. Western blot analysis showed unchanged expression of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2a) and phospholamban, associated with upregulated Na(+)-Ca(2+) exchanger levels following acute methamphetamine exposure. In addition, methamphetamine promoted overt cardiomyocyte protein damage evaluated by carbonyl formation. Taken together, these results demonstrate direct cardiac depressant effect of methamphetamine in myocardium and isolated cardiomyocytes, possibly associated with protein damage and dampened adrenergic response.